To me the main issue with the market is that it's very difficult to link up buyers and sellers. The only way to express your interest in buying or selling a resource is to create an order. There are two issues here:
The limit of 50 orders is totally insufficient. There are 42 resources, so you can't even have 1 buy and 1 sell order for every resource. That's before we even think about multiple rooms (which will be needed, because the market is localised).
Orders are subject to a fee as soon as they are created
These issues seriously discourage creating prospective market orders. I have some LO to sell, but I'm not going to create an order because I can't afford to waste one that might never be fulfilled. I have no idea if anyone is interested in buying, or if there is, I have no idea what price they would buy at.
If I do decide to create a sell order, what price do I start with? How long do I wait before lowering the price? Has it not sold because I'm asking too much or because there are no buyers right now? What amount should I place the initial order for? If I create an order with a small amount to see whether anyone is interested, perhaps no-one will buy because they don't want to waste a terminal cooldown on such a small amount. If I create it with more, I'm wasting more credits if no-one buys or I have to reduce the price.
Both issues discourage creating orders in the first place. If I do create an order, the up-front fee with no refunds causes orders to be placed with tiny amounts, even if I have 500,000 resource to sell.
This is what slows the market down, and it's particularly bad for less popular resources like middle-tier boosts.