The server could act as a player in the market to reduce spread (difference between buy and sell orders) and at the same time suck gold out of the system. If this was properly implemented, it could make market more usable (almost always kind of reasonable buy and sell orders in place) and suck more gold out of players' pockets than taxes ever could.

The idea could work like this: whenever any card has a 30% or higher difference between the lowest sell order and the highest buy order, the server could place buy and sell orders for it that reduce the spread by 40%. 10 units of that could come from the buy order and 30 from the sell order. For example, consider Pine Ent, that currently has a ridiculous lowest sell offer of 249 and a highest buy offer of 74. In this case, the server would place a buy order at 91, and a sell order at 196. Yes, that is still a silly spread, but I could imagine taking those offers if desperate.

To make absolutely sure the server wouldn't be buying too high or selling too low almost ever, it could keep only 0-6 of each card and not sell if it has 0 (of course) or buy if it has 6 already.

To be clear: the server would NEVER make "market orders", that is, buy cards at a price someone has put a selling offer for, nor sell at a price someone has put a buying offer for. It would just make a bit better offers for cards that have only ridiculous offers and wait. If people take the offers, the server would be buying low and selling high, eventually getting gold from players. Everyone would benefit in the end, except people with the ridiculous offers.

This could of course be done manually by the administrator too, but if the strategy is careful enough (the above system should be), it could be automatic without artificially manipulating prices.

By the way I bought gold, spent most of it on boosters and put almost all of the cards I got on sale. I also placed a lot of buying orders, so a lot of the cards have a smaller spread now than before.

Creating trading bot doesn't worth a try until there are players in game.
When they will be there market will balance itself, and only if it won't there's a reason to create bot.