A lot of the bullshit that comes with owning your own business, particularly in a creative field like photography and design, is the sort of bullshit that you have to take as it comes and grow/develop in response to said bullshit.
It would be very difficult for me to give broad advice to somebody looking to avoid being taken advantage of because it comes in all different shapes and sizes and some people have their own idiosyncratic ways of ripping people off. That being said, I'll try my best.
My biggest issue early in my career was being too passive and not standing up for myself when I should have. This issue persists today, but I have gotten much better at being assertive and professional. I will list a few of the issues that I had early in my career that come to mind.
I was hired by a company to shoot an event. It was a big event and I had a lot on my plate, so the company included me in an email chain so I could discuss the details with about 6 other people who were running the event. On the day of the event, all went perfectly until the very end, during the dinner part of the event. As I always do during events, I very quickly snapped a shot of the food. Very rarely will a client ask me for shots of the food, and very rarely do I actually send them, but it only takes a minute so I make sure to do it, just in case. Sometimes a vendor asks, sometimes not, but it's safe to have in my opinion. While I was shooting the food, a very stern and aggressive man comes up to me and tells me in a hostile, scolding tone that I shouldn't be wasting my time shooting the food. I was around 23 at the time and he must have been around 50. He could obviously tell I was scared and began shadowing me for the rest of the event, occasionally telling me what to do and not to do in a very hostile manner. I immediately approached my main contact at the company and told him about this man who was not on the email chain. The client told me to ignore him but it was difficult as he had such a hostile, intimidating presence. His actions made me nervous and stressed and definitely impacted the quality of my work from that point on.
If the same thing happened to me today, this is how I would handle it. "Excuse me, sir, what is your name? I am sorry but you were not included on the email chain and I was not made aware of your responsibilities here today, so if you would not mind, can you please speak to my client about your concerns so I can address them accordingly?"
Another small issue, but an intimidating one happened about a year later. I was hired by a company to photograph behind the scenes at a fashion show. This meant being in dressing room while models changed. At one point security yelled out "Everybody must exit the dressing room except models". I did not leave. One large security guard approached me and asked me to leave. At this point I was a bit more used to this sort of pressure and responded accordingly. "I am very sorry, sir, but my client hired me to photograph the dressing room and I am unable to leave until my client tells me to leave." Another guard approached me, followed by a third. 3 grown men against a young photographer. I repeated the same thing as they grew more hostile. My client eventually came and told security that I was OK to be there. This was after several minutes of intimidation.
Now to the good stuff. Some people make strategic friendships throughout life in order to reap the benefits. These people are not looking for friendship, they are looking for the benefits. This has happened to me a few times. I do like making friends with clients, but don't like when they expect to gain from our friendship. As soon as that happens, I begin to feel that they don't want me as a friend at all, and as a result I often wind up resenting them. If a client wants to befriend your brother, that's great, but he should never lower his price from the first shoot, or increase the services he provides for the price. As soon as he does that, they will expect more and more each time and he will eventually lose them as a client and an acquaintance. I should note that I do have many client friends and not all clients befriend photographers in order to get better prices. The bad guys are few and far between. It is never good to be bitter or untrusting, but your brother should be aware that these people do exist.
Contracts!!! Every client should sign a contract prior to working with your brother. For many types of work, your brother should require at least 50% down prior to the shoot and the remaining 50% after watermarked proofs have been sent. Upon client approval, the watermark can be unlocked. Before I required a 50% retainer, I got cancellations much more often than I do now. Before I required the remaining 50% prior to delivery of the photographs, I would often have to remind clients far too often that they owed me money. Asking somebody for money over and over again is not fun and will not make somebody look upon you in a positively light. It turns a photographer into the likes of a loan shark. Get the money first and avoid this problem altogether. Many companies will have 30 day accounts payable. For legit companies, this is fine with me. Many of them will not budge on this but I have never had an issue with this.
Figure out a shot list prior to the shoot, and include that in the contract. I had a client reach out to me some time ago asking for promo shots and portraits for his company. The quote for their shot list was around $3000. He wanted to spend $700. I worked with them on honing down their shot list to accommodate a budget of $1,000. We cut the shot list in half and removed the portraits. Prior to writing up the contract, I emailed him the amended shot list and he approved it. I then put the same shot list in the contract and they signed it. When we wrapped up with the shots, I offered to do quick and free portraits of him and he agreed. I told him in advance that they will be very quick and he can take them or leave them, but I thought it would be nice to give him a little extra.
First I delivered the set of photos from the shot list. I got, in writing, a response that said how great the shots are and how everything is just perfect. Then I sent the portrait and I got an email followed by a handful of missed calls. I immediately checked the email and it said that the portrait is "unacceptable". I then called him and he was very mad, insisting the portrait is unacceptable. I reminded him that we agreed upon a shot list and that the shot list did not include portraits. I forwarded him all pertinent emails about the shot list. He then started with the whole "I am the client and I will get what I want" thing and I turned into a robot. "I am disappointed to hear that the portrait is not acceptable, but this was a free gift and not a commissioned photograph, so you do not need to accept if you do not like it." He threatened legal action, and eventually stopped calling. A couple weeks later the portrait I took was featured prominently on his website. Apparently, it was acceptable. A client like this just wants to get money back after the fact, and you'd be surprised how often it works. Some people complain about their food at every restaurant they go to. Most restaurants will offer a refund if you complain enough (not that I have ever done this, even when my food is shitty). For people like this, it's no skin off their back to complain, threaten legal action, etc. When they realize that they won't get what they want, they will typically back off.
This story is one of my all time worst moments. I had a client who asked me to do product photographs. We agreed upon $1,000. He arrived with a check for $250, I did the work, he said it was great, and then he gave me another check for $250. There was a language barrier to a degree, but we did agree upon the price in writing, but I was intimidated to address it, so he got 50% off. He then hired me again the following year and I made sure to do a contract and be extra clear about the rate. Again, it was about $1,000. He paid $500 up front. I did the work and emailed it to him. I have, in writing, emails that say "These are amazing. Perfect as always!" and so forth. He must have just assumed that he would get 50% off again because as soon as I asked him to mail the balance to me, he started complaining. Things like "These photographs are not good enough and of no use to me." I also reminded him of the fact that his previous emails used words like "amazing" and "perfect" and that he already had the images on his website that were being used to sell the product.
He called me and was yelling and cursing a lot. I told him I am no longer able to speak to him on the phone due to the hostility but that I will promptly respond to all emails. That night I got literally hundreds of missed calls and dozens of voicemails. They started angry and turned into nothing more than screaming. I also started getting texts saying "I know where you live!" which scared me and made me look twice whenever I walked out of my front door.
I still had about $700 worth of his products and told him I could not mail them back until the balance was paid, as per the contract. With continued hostility and threats, I informed him that I could no longer answer his emails until the balance was paid, seeing as he did not agree to remove my photographs from his website. He finally realized that he was backed into a corner and told me he would come to pick up his products. I told him that he no longer had the opportunity to meet with me in person due to his threats, and that he would have to pay for return shipping.
3 weeks later I got this voicemail: "I am so sorry about everything that happened between us. I was going through a very stressful time in my life. You are a great guy and you take great photographs. I am very sorry about the way I treated you and would love to work together again."