from a technical standpoint, the mere procedure of tracking a click is irrelevant for comparison of the different accounting types.
it is likely, that tracking or circumventing a cpc click is equally feasible to tracking or circumventing a click that starts the tracking history for a cpa paypout. that's why i was not referring to this. you should read more carefully.
have a look at the conditions under which the user successfully responds to an ad:
1. he notices the offer
this is independent from the accounting method. let's assume that an offer is noticed in this case.
2. he clicks
this is a needed condition to get credited both for cpc and cpa. under a cpa environment, a click is the starting point of the tracking mechanism for potentially getting credited. whereas if the user clicks under a cpc environment, the job is done and the publisher gets paid.
3. he buys
this user behavior is only mandatory under cpa conditions.
step two is essential for a cpc payout. steps two and three are essential for cpa to credit the publisher.
conclusion: a cpa payout is dependent on a more vulnerable two-step-procedure. there are the numerous mentioned distortions which hinder a proper attibution of the sale to the advertising effort of the publisher. this was the point i was referring to. there is much more trouble for proper cpa tracking.
but anyhow, my main objections concern the non-technical (because in no case trackable!) issues when a click has already been executed, such as purchases with no tracking history, orders from different access points etc.