How the F*** is it that they seem to think what their new members/subscribers/enrollees do/choose not to do AFTER you've delivered them per the terms of your agreement (and they're well beyond the point in the sales funnel that you see any profit from) is somehow YOUR responsibility - and Why would your network, presented with such a childish complaint / threat of nonpayment, even entertain the idea that it's "your fault" long enough to consider bugging you with it to begin with?
The way I see it - They got what they paid for long before the basis of their complaint existed....
They Paid you for: Real Human Visitors, providing valid email addresses/verifying email addresses, etc. I'm assuming in exchange for whatever giveaway/trial/sweepstakes it was that they were offering at the moment...
From that point on, they handle the remaining segments of the sales funnel exclusively, Because they choose to go the route of ensuring they keep as much of their sales profits as possible, also implying that they are confident in their ability to maximize the value of any leads produced by you (or other affiliates) , or believed that they would gain a higher profit by handling that portion of the funnel on their own vs having affiliates see it through and therefore give up a larger cut of the resulting profits ....
Based on the above, they made a decision that your efforts are not deserving of being compensated beyond the point of a modest e-mail submit compensation (It's NOT rev share)....
Your interest, involvement and accountability in the sales funnel therefore ends at the same point in the sales funnel as where your compensation ends....
If they were experiencing the opposite end of the ROI spectrum and converting VERY WELL, do you really believe they would track you down to offer you Rev Share for the amazing leads you provided ??? F*** NO!!! They would be glad they got rid of you at $0.8-$2/e-mail submit and enjoy their loot....
If you've done your part ethically, provided actual human visitors, who were not microworkers/turkers, and who submitted and validated legitimate email addresses (or whatever was specified in their own offer for you) and who were not incentivized (unless they allowed incent traffic, then it doesn't matter whether they were or weren't) YOU HAVE COMPLETED THE JOB FOR WHICH YOU WERE PAID.... and your earnings should never come in to question beyond that point
If you've provided them exactly what I just described - YOUR PORTION OF THE SALES FUNNEL IS CLEAN - and a "lack of sales" therefore is less likely due to their claim of "low quality traffic" and more likely a result of a "low quality back end offer/product/poor sales page or offer" on their end....
They want to cut you off from compensation beyond the initial email submit, yet hold you accountable for the actions or lack thereof of the customers 3 steps beyond any involvement on your part with the process... RIDICULOUS - They can't have their cake and eat it too - classic case of a refusal to take accountability, and a refusal to accept and therefore LEARN from failure on their part, which is why that "advertiser" is destined to fail.....
Just my take on it (not that anyone asked, mind you)