Robert_Charlton - 6:35 pm on May 18, 2013 (gmt 0)
I generally do whatever I can to discourage SEO clients from having affiliate programs. There are some exceptions, but they have inevitable complications.
In B2B areas, eg, where specialized affiliates are established as part of niche distribution networks, I have clients include contractual prohibitions against copying site content... and also to create a second set of marketing material "just for affiliates". It's usually not enough simply to tell affiliates that they shouldn't copy. Without the alternative content, the writers they hire will paraphrase.
The very best affiliates needn't be told not to copy, but they're rare. On the other hand, the very best affiliates may well end up outranking you.