I think it's shady. I list all repairs made to a pipe if I sell them. Minus the basics. Light tooth chatter, stem deoxidizing, etc. If those pipes are re-sold, that's another story.
If your seller is the repairman than the pipe mud was knowingly used to cover a crack and should've been disclosed.
If your seller is the repairman than the pipe mud was knowingly used to cover a crack and should've been disclosed.