I don't really think DP buy sell and Flippa could be compared; mainly because they have different models. DP does it free while flippa charges. From the experience of using both; I think DP buy sell is good for hiring/offering small-scale services e.g. marketing, seo etc. Whereas flippa is good for selling websites specially; I had good success selling websites there (2000+ price range).
Depends on how you want to sell: DP is 100% free, flippa is not. Flippa gets slightly better exposure, DP gets a bit less.
Dp works best if you don't like/don't want to pay a fee and you know exactly what your site's value is, since it's a forum of webmasters (more or less) and they generally know what is worth the cash and what not. Flippa is better known for selling sites , so probably there are a lot of unexperienced buyers there (also lots of scammers).
Just so Everyone Knows...I have the Middle Man...A good cross between over between Flippa and DP. Although I use them both, I really miss the OLD SitePoint Marketplace. So I have been developing a NEW Marketpplace. Our site Will officially Launch 11/11/09. No we are not a FLY by NIGHT outfit with a cheap script, we have invested tons of money into this site. If your interested please send me a PM. Ill give the first 10 people 50 FREE credits just to try our site. YOU WILL LOVE IT, maybe not as much as DP but it will give you an alternative to FLIPPA. Thanks Tommy
I think the interface has a lot to do with it. So much easier to find/see listings on Flippa than it is to do here. I'll also second the vote on being more likely to scammed on Flippa than you are here.