Are we talking about markets for buying goods or exchanges from/to fiat?

If you are talking about a market for items, this setup is bizarre. Why would you have a server generate your keys, ever? Key generation is not something you trust to anybody.

The correct way to do this is to use 2 of 3. Each purchase needs three keys: buyer provides a public key, vendor provides a public key, market provides a public key. This is then used to create an address for payment for each sale.

Market gets hacked? They only have one signature. You get hacked? Only one signature. Vendor hacked? Only one signature.

Normal transaction? Market signs tx to pay vendor, vendor completes tx with their signature.
Cancelled order? Market signs tx to refund buyer, buyer completes tx with their signature.
Disputed transaction? Market signs tx, gives to buyer or vendor to complete depending on situation.
Market obliterated by aliens? Tx is signed by buyer and vendor, in whichever order works best.

Main problem: people tend to lose their keys. Don't ask me how they lose important stuff like that, but it is the main problem.