Backlinks? What do you think?

Hey fellow SEOs. I do a lot of content creation, internal link building, site architecture management, keyword research, PPC/SEM, analytics across the board.

I haven't done the played pay-to-play backlink game, though I've been offered compensation for linking dofollow links back to sites (haven't ever moved forward).

What is your experience with paying for backlinks? Obviously reputable sites, obviously pages that make sense. Has the deal ever gone bad? Do backlinks ever get removed? I know it can be a tightrope.

I've scoped a few marketplaces but haven't found too much advantage over another. What marketplaces do you recommend?

Thanks SEOs