There really isn't a way to know for sure, you can look at stats all day long and see that you got hits, even if you get a sale, you could still be getting skimmed.

Just have to cross your fingers and hope for the best.

Five years ago I signed up for a site that I really liked through my link (wasn't against their terms at the time) and stayed with them ....got paid 50percent at signup, got paid rebill number one, got paid rebill number two, but did not get paid for rebill number three....so I cancelled my membership and stopped promoting them.

I also promoted a site I'll call ABCX.
I used to make a sale with site ABCX 1 to 3 times a week EVERY week.
Site ABCX added a few new tools to their affiliate program and for some reason I never got a sale with them again (not even the rebills), even though I was getting about the same number of hits to their link.
In their terms I can't do a test signup, so I deleted all my links to site ABCX.