<Meta>: I am not really sure whether to tag this as existing feature, new feature, or rebalance. I chose rebalance because it is more like overhauling/adding on to the entire store completely.
Currently, the Black Market is a place where players sell items more than the market price to earn a profit and that they often fail to earn, simply because players do not purchase items priced higher than the market price.
So here is my suggestion: Make the market free from the static prices they are currently in.
This essentially makes it so that to sell an item, you would have to price it lower than the current market price currently is. Players can opt to earn some money back by selling or by deleting said item.
Usually, TF2 market prices are deduced by voting for their prices by the TF2 community. These prices come from proof of sellers who sold these items at their lower/higher price.
Games like Offworld Trading Company automatically deduce market prices by the 25 units sold at their average price.
My opinion: I would recommend automatically deducing market prices for lower tier items as the community do not care about the items the receive from lootboxes/do not care about the economy. TF2 market price voting is already voted by a thousand or more people, much less ours.