getting listed as an "related site" in whois query.

I was ran a WHOIS query today on a forum that discusses a niche product i'm about to sell. I used Domaintools and a part of the info it gave me was "related sites". There were three. One established company that sells these products (that is cunningly deceitful), One spammy as all hell web-site that sells them and the site of one dodgy merchant that sells a bunch of crap that is unrelated.

So I'm wondering, Does anyone know what these sites did to get them listed as being "related sites" in domaintools.com's WHOIS ?

How does it affect SEO ?

It may be because of the three websites sharing the same ip address.

thanks, just checked. none of them do. and this "related sites" field only shows up for some sites when i run A WHOIS on domaintools. I had never seen it before.

can anyone else hazard a guess at what's going on ?