Yes they do encourage refunds a bit too much! I am a vendor and sometimes when customers contact clickbank asking for tech support (help in downloading etc), clickbank support would ask them "would you like a refund today?" without the customer even mentioning it!
That being said, I have noticed that high refunds do generally mean crap products. There are products on CB which promise the buyer to make thousands daily on autopilot; which unsurprisingly do not deliver and hence high refunds. On the other hand, genuine health products tend to have very low rates; although there aren't many of them.