If someone asks me to submit a recommendation on their behalf, I usually do, but I always do it honestly. We don't have a lot of pilots here, so I would like to reduce the chances of flying with a turd as much as possible. That being said, it would take a lot for me to submit a recommendation (especially a "do not" recommendation) for someone who did not ask me for one...probably a major integrity lapse or something along those lines. Still, I've thankfully never even considered it. On a side note, the most mediocre recommendation I have ever submitted still got hired - then bailed in the first couple of months for their "dream" airline. I guess the moral is if you honestly believe someone should not be hired, don't try and be subtle about it.