I usually handle it case-by-case:
If I get the feeling that the post solely exists in order to transport the referral, I flag it as spam.
If the post seems useful to me, I remove the referral, leaving the link without it.
Putting referral links into posts definitely casts doubt on a user's reason to post. I couldn't find an official rule, yet, but it is along the same line as posting your Bitcoin address for tips in posts. We forbid that, and other signatures, except in your personal profile. I'd say, let us put it in our rules officially.
To add some reasons (Update on 16th of December):
- I'd consider it bad manners to put something in a post in order to profit financially, while the whole site is based on community effort.
- Many if not most answers that include referral links are solely posted to present said link, therefore it lowers the perceived quality of a post when I discover a referral link in one.
- "When I (significantly) improve a post with a referral link, should I change the link to my own referral link? Why should another profit financially from the improvements I made to his post?" -> Allowing referral links opens a can of worms.