I personally check NameBio for sales data prior to any sale or purchase. It's a fantastic tool and provides unbiased sales data. @Michael has done an awesome job keeping the data as accurate as possible. Anyone making a sale without atleast checking Namebio.com is doing a disservice to themselves and possibly leaving money on the table or paying too much. Just today, I was in negotiation on the sale of a domain. I paid $1000 for it a few years ago and someone made an offer to purchase for $10,000. If I only went by what I paid for it, it would have been a "shoot the moon" sale! 10X on a $1000 investment..in under 2 years. But as I always do before any counter offers, I check Namebio.com and I noticed that most sales with the keywords that my domain had were in the 30,000 to 50,000 range with a high of $165,000. Needless to say, I countered with a much higher number and did not accept the $10,000 offer. Everyone do your due diligence before any purchase or sale! And thank @Michael for keeping Namebio.com free!