I'd disagree about Flippa, but agree about Ebay. I speak to a lot of 'serious' buyers and whilst most of them will point out Flippa's flaws, they will still keep a regular check for relevant purchases.
I've seen mid - high end (+ $10,000) sites in evergreen niches selling for an average rev multiple of 10.2x (current average is 7.6x) with web apps that have good proprietary software and some proof of concept (revenue) selling for much more.