Drama Regarding Marketplace Disputes

A lot of communities have a marketplace section where users can buy and sell services, engage on trade, etc. Sometimes when a party refuses to go by the commitment or a offers less than what was promised, drama might arise. Do you see marketplace dispute dramas in your community? How do you handle such dramas?

I've had a couple of minor issues on marketplaces on a couple of forums but I've never run a forum where there was any issues. I usually put something in the guidelines that use of the marketplace is at the user's risk and no staff will be accountable for any issues.