I've been thinking for a while now there would be a cool feature to have an exchange shop.
To clarify what I mean by exchange shop, it would be a same principal shop as a normal store, but instead of ordering supplies, people would have to come in to your shop, and sell the stuff to you. The exchange shop would sell stuff like bobby pins, radios, all of the stuff from a normal store but of course, cheaper. The principal of this exchange shop would be that people can sell they're bobby pins, and other unwanted items to the shop for some price, and where as the shop owners could resell them for a little bit more. This would increase and make the server economy better and people would stop having hundreds of unwanted items stashing in they're houses. There would be a little more of a competition between stores.
Also realized, that in the server not every GTA V store is scripted, so the ones which are not scripted, would be perfect to make the exchange shops.
Basically in summary, exchange shop would be that people can come to sell stuff, and then they would come up on store for other people to try to hunt good deals and buy stuff.