The primary way to eliminate any of these “tire kickers” is to manually approve affiliates as they apply to your affiliate program.
You should apply some sort of criteria to prospective affiliates to be sure they are affiliates you’d like to have in your program.
Take a look to see if they seem to have a relatively fresh site that they are updating often. Check whether their sites are ranking well for key terms in the search engines, and if their content is relevant to your business.
Another approach, which is going to piss off a lot of affiliates, is to conduct a periodic audit. If affiliates don’t respond to your various efforts by phone, e-mail and direct mail to make them active, you could always just remove them from the affiliate program.
However, that’s not the best approach. You’re going to sour some potential producers by effectively rejecting their sites after you already accepted them.
While you point out that it doesn’t cost anything for affiliates to join your program, it also doesn’t cost anything to keep them in your affiliate program.
Ideally, scrutinize who you let in on the front end, and it should alleviate your “tire kicker” issues.
Personally, I think a good measure of whether an affiliate program has too many affiliates is whether you can adequate support the number of affiliates you have.
if you are not getting back to their questions in one business day, and providing support on other issues on a timely basis, you need to staff up or audit down.