By all means ask people for the words of their best songs, but don't come stomping in to their regular venue the next week and sing it in front of them.

Good Lord, yes. I've picked up three or four songs from a regular at my local session - somebody who's been going to folk clubs for, at a rough guess, 34 years longer than me (admittedly I was a late starter). I've only done one of them in front of him; in fact one of them I've never had the nerve to sing out at all, it seems so very much his song.

I used to be into looking songs up & going back to the oldest possible version; this was partly because I picked up a lot of songs from what were basiclaly folk-rock recordings, which meant that I had to do a lot of work on them to make them work unaccompanied. These days I'm much more likely to take songs from recordings where they're sung unaccompanied or nearly, so I don't bother so much messing around with them. Messing around with versions of Child ballads is always fun, though.