At Flippa you can never tell. I've seen some sites with almost nothing on them sell for quite high prices and I could not figure out why someone wold even buy it. Some others that would seem to be a good investment and that are selling at 3-5 times monthly earnings don't sell. I've actually just started selling some older sites on Flippa so I don't have much personal experience yet, although I have read a lot about the technique over the years from domain and site flipping courses.