This is 100% correct. A lot of dealers start off buying double or more of what they need, and selling the rest to break even or make a buck or two. They start by selling to friends and family, kind of like a group buy that they organize. Eventually, either because they want to make more money or they want more product to themselves (or a combination of the two) they start taking in more people. Say, friends of friends.

This process tends to snowball. Because their core group is most likely all friends, family and friends of friends, the rest tend to not get messages back in a timely manner or at all. It's not because they are trying to be rude, but because at the end of the day what they are doing isn't exactly legal and you are ALWAYS going to be a liability. Any time they re-up they try to hit there break even or money goal with their core group, and then start doing sales past that if they haven't reached their goal yet.

Not a lot of dealers buy and then just sell as much as they can until they don't have anymore. The ones that do typically are the ones that hit you back instantly and are always ready to do a drop. These are the dealers that are further up the chain closer to the supplier, either being the supplier themselves, or working directly with them usually.

The chain (now a days) usually goes Supplier->Dealer A->Dealer B->Dealer C

C Dealers tend to be that guy that might have some sometimes but it's expensive and as a last resort dealer. Most of the time they don't even consider themselves dealers.

B Dealers are the ones I described first, of which there are a metric ton of.

A Dealers are where you want to be getting your stuff from, as the prices are cheaper (especially as you get higher then buying just a gram or a 8th) and they typically respond faster and are more supplied. Because they offer prices breaks for bulk buying, people that find A dealers and get good deals often turn into B Dealers themselves with the process I described.

There tends to not really be D dealers anymore, as there isn't a lot of mark up in most areas. 45 a 8th/15 a g has been the gold standard for pricing for a while and it most places. If you under those prices you are getting a good deal, over, a bad one, but of course it fluctuates per area.