I'd say sitepoint is great.. you can feature your listing, have it listed more prominently.. etc I find on DP that your site dissapears to the 3rd - 4th page within a day of posting..
Looking at the other listings for domains on sitepoint, it does not look like the best site for selling domains, but for actual Web sites, there looks like a lot of good potential for sales.
While we don't play judge & jury in disputes, there's plenty of things you can do to protect yourself - starting with doing research, getting real contact information for the person you're dealing with, getting a contract and using something like escrow.com . All that being said, we're progressing quite nicely with the development of additional security features to weed out undesirable marketplace participants.