I have had a few times when I was contacted out of the blue on a hook-up site by guys who said they "had heard from a friend" I have a hot hole or give good head. I usually looked at their profile and if I liked what I saw we got together. If it was one of those profiles with hardly any info I asked who that friend was to know what type of guy their "friend" was. No reply, no hook-up. If they did give me the name (= chat name) I would consider it. If I could remember who that was...
Back in my student days when I was out clubbing I sometimes was hit on by guys who said "So, you're a friend of ***?" When *** was just some guy I had fucked with, not a friend. I knew then what it was they where after (easy NSA fuck). If he was cute (I was more picky back then) I went along with it, horned up, knowing what would happen after closing time. Easier than having to cruise for dick after everyone was thrown out at 2am ;-)