It seems to me people want to reconcile two conflicting expectations:

. Players that want to buy something would like that to be easy: search feature, hand-holding to seller location, remote delivery, and so on.
. Players that want to sell something would like to make a profit (over the cost of farming the item) through high price, or sell fast (or provide a service to the community, making the item available and not hoarded/left in used tab) through a low price.

A reseller would undercut people selling too high, and prevent fast sales or the community service by buying items that are priced too cheap. If you try to prevent that by making it difficult for players to sell, or to buy, people complain. If you make it easy, people complain as well (maybe not the same people of course).


Now for suggestions:

- There could be a fixed player price, i.e. in stalls you can only sell or buy at that price, and it's driven by the economy: when a new item is on sale and previous ones didn't sell much, the price goes down automatically. It goes up if the same item sells fast, and eventually the price is balanced.
Pro: no reseller.
Cons: need some code and 99% of the players are probably going to hate that.

- What we really want is not to make selling or buying difficult, we want it to be difficult to automate:
. put a limit on the number of items one can sell or buy,
. introduce a bazaar time window (say 1h) when you can buy followed by a cooldown (say 10h) when you cannot.
Again, 99% of the players are probably going to hate that, but you wanted suggestions!