Currently, many players are dependent on vendors, especially produce vendors, and will often buy produce from them, rather then the auction house. Many players, suggest simply removing the vendors completely. However, this will cause new players to be VERY disadvantaged. So I propose, that vendors remain. BUT, instead of unlimited stock, they only have the stock sold to them by players.
There would be a limit of perhaps, 500(?) of each good. Players would sell there good, not through the 'sell' menu, but a new menu called 'supply'.
The prices of the goods cost/purchase price would depend on the amount of remaining stock. Ie, A large amount of stock, results in a lowered price for both buying and selling. And vice versa.