Webwork - 1:20 pm on Sep 4, 2010 (gmt 0)
A standard practice in the domain industry is to "test the traffic" by having the domain name repointed and paying a reasonable fee for the traffic test period.
Reasonable fee? That depends on volume, target industry, source of traffic (type-ins vs. old links vs. spammy domain promotion links posted out in the wild, etc.)
Once the domain is pointed you can begin to analyze the traffic sources, quality, etc.