Building trust with your audience is paramount in affiliate marketing, and the quickest way to lose trust is to recommend products either you haven’t used before or that aren’t a good fit for your audience. Also make sure you never tell anyone to directly buy a product, you are simply recommending the product. The more helpful you are and the more you make quality recommendations, the more likely your web visitors will come back for your expertise.
In the case of cost per mille/click, the publisher is not concerned about whether a visitor is a member of the audience that the advertiser tries to attract and is able to convert, because at this point the publisher has already earned his commission. This leaves the greater, and, in case of cost per mille, the full risk and loss (if the visitor cannot be converted) to the advertiser.