I would say there's not a lot of real, valuable sites on Flippa but they do come through. Sites of lower prices do have a better chance being legit but there's also a lot of worthless sites created just to sell. If you have a website with real, verifiable income, you can get $10,000 for it, you just need to prove it.

If you sell it within the first year, you probably can't get more than 4-6 times monthly revenue (not enough history). If you've got 12 months of revenue history, the prices start going up and solid sites get 10-12 months revenue etc.