Well, perhaps you should first be sure that they did not acquire a license to use the script. There is no way to tell by looking at a site whether a license was purchased or not.

For instance I always encourage people even on commerical sites to include the link to Gossamer Threads even if they pay for the script. I myself have a few clients who purchased a license but I still included the link within all script pages to give credit to the script and encourage others to use it.

Is this how you are determining whether the script is being used for free?

Unoffical DBMan FAQ

http://creativecomputingweb.com/dbman/index.shtml/