Hey stuartbaggs,
Well, my take on the whole thing is this:
What would make him follow a link you provide anyhow? I mean, let's look at things realistically here...
1) He screwed you on eBay, and presumably, he knows he did that to you.
2) He knows your email address.
So, if you sent him an email with a link to click on, why would he follow it. You would have to be pretty convincing, and if it were me, you would never convince me a link you provided was safe.
If you sent it from a different email account, he wouldn't know the address, and would just dump the email without following the link anyhow (probably).
If you masked your email as some "official" looking email from someone (like eBay staff, PayPal staff, etc.) then your actions would be illegal... Essentially, what you are asking is bordering on illegal, depending on why you want that info anyhow...
Just follow the advice of Zib and Drak, and go to eBay with your problem... If you were screwed on merchandise, and payed using a CC or PayPal, you can dispute things. If you were the seller, then go to eBay, and dispute as the seller.
Lastly, here where I live, the local news stations have been known to get involved, and have helped resolve things on eBay before, in the past with very good resolve, but no matter what, you should definitely proceed with this only when you have gotten eBay involved, and exhausted that resource...