atlrus - 1:10 pm on May 19, 2013 (gmt 0)
On the other hand, the very best affiliates may well end up outranking you.
This is probably what you should be most afraid of.
In cases where I work with aff programs, the vendors are not suffering from Google penalties, despite the affiliates being high-risk high-reward (i.e. nothing is of the table to chase ranking), but some weak vendor sites are badly beaten by the affiliates.
On the other hand, if the vendor is really smart, they use some of the affiliates to help them rank and have done a good job.
My 2 cents, for 5% increase in sales I wouldn't even bother. I would rather spend the projected affiliate expenditure for advertisement of my own site.