I think it would be nice if the auctions were a bit more interactive. Perhaps It could be more like E-bay. People could decide how much they want to put the starting bid at and when they want it to end. Also, people could get the final bid on their object paid to them, instead of some pre-chosen amount when they first post it. There could even be a buy-now. Also things like upgrade crystals, npc trader cards, etc. that you can as of right now sell but not buy on the auctions, should be able to be bought as well.
I believe it is due 'Silver Fraud' as it was quite prevalent back then in Travian Legends, someone would put up an object at X time and then the silver bot would bid on it resulting in crazy amounts of silver for an item that would normally not exceed 500 silver or so.
Due the above, Travian decided to give sellers an average silver price up front that is calculated from a first 5 items stack put up by the system and then after that by the average silver value that is being bought on the auction.