I had a guy request a custom version of a small, fragile, mostly glass item I make. He wanted a giant one, so I accommodated him, special ordered parts, built the thing... Cost almost as much to ship it to him as I charged him for the item, so grand total around $200. He was very happy with it when it arrived.

Almost a year later he messages me saying he wants me to make two more, so I contact my suppliers and one of the parts I used to make the last one is no longer available locally, so it'd cost a little more to ship it in from somewhere else. I relay this to my customer and he sends me back a big long message about how I should be grateful for his repeat business and I should give him a 50% discount and free shipping... for being such a good customer and "doubling the size of his order." He insists there's no way it should cost MORE to make the same item.

I had to reply and tell him I couldn't take on his special order, and unfortunately an increase from one to two, while technically double the business, isn't really something that pays me for my time + materials based on a year old price, and after a 50% discount and free shipping. I have no control of the price of things I don't keep in stock, and I'd be paying out of my own pocket at that point to make these for him.

He was beyond angry and I ended up having to block him. I still can't imagine why he thought I'd go for his proposal. He didn't even offer me exposure. /shrug