I am not a merchant so I don't know some of it, but it would be nice to up the amount of auction slots as well as lower the auction fees which should see more competition from people trying to sell things. I would also like to see higher storage amounts as well as 500 slots can be filled rather fast as you start collecting things.
I think it would be a good way for MA to make additional revenue by allowing merchants to get more auction slots. Start with maybe 10 Ped per extra slot and every 10 over that up it 5 Ped or something as players head to a maximum cap for auctions still. It could either be a one time fee, or like a monthly fee were after a month has passed you will loose the auction slot and have to purchase it again. Depending on the price it could be weekly as well.
It would be nice if they changed the auction fees to a % of profit over the TT value, and allow auctions to be bid on in pec as well so new players could more easily sell their hunting gains without taking such a hit. So if someone sold something for just TT value they wouldn't get penalized. I know this isn't the best idea and would probably cut into their profits, but smaller players loose a lot of Ped setting up auctions for stuff to only be sold at 100% when they might be able to get somewhere between 100-101% if it could be bid on in pec. Changing the fee to the above idea would allow smaller players to be able to post auctions instead of having to spend a ton of time either finding a merchant or just TT their small amount of loot. It possibly keep them playing more and not stopping because they are frustrated because they are loosing so much doing small hunts and trying to sell it on the auction to get a little MU back only to loose even more.