Never "trust" any ONE stat when buying traffic. Look at the objective stats first like Overture with extension, alexa, see where its linked by searching for the whole domain in google, etc., etc. Then see if they're Kosher.
A domain with a high alexa and really no or low overture with extension is a red flag.
This is a good easy to read article about how to buy traffic:
http://www.namenewbie.com/How_to_Fin...g_Domains.html
Looks at all the basics and tells you what each score is worth.