This is known as "shaving" among affiliate marketers and it mostly doesn't matter. E.g. when you are choosing among 10 offers to monetize your traffic, you split test and keep the one that brings you most money, regardless of whether advertisers are honest or not.
We try to do this automatically. If a product attracts clicks but doesn't convert then we disable it temporarily, to give other products a chance to be shown in their spot.
So if the retailer is cheating, then their products should not be shown very often - and products that do convert should be shown in their place.
