Frankly, I think referral (or affiliate) links should be nuked on sight.
Okay, sure, there's disclosure here, so nobody's being tricked. But what if that leads someone to post another answer to the same question, perhaps with some more detail so it's more valuable, with a referral link of their own? It's a better answer, so why shouldn't it stay?
More likely, someone posts a good answer that contains a referral link, but six members of the community flag it as spam. Then that answer owner comes over to Meta to complain that their post was wrongly flagged, especially since here are these other answers that also have referral links. Why haven't they been deleted/flagged? Where do you draw the line? How much disclosure is enough? How much detail in the answer is enough? Is each person allowed to post one answer with a referral link? One link per service? If I post a lot in the Dropbox tag, why can't four or five of my answers have referral links?
No, I think allowing referral links is more trouble than it is worth.