They do have certs and the owner can rig and derig their own glider. Well anyone can rig and derig any glider as long as they've been shown the salient points. I had to derig the club K8 after my 50k downwind dash. It's suprisingly simple, gliders are designed to be quickly rigged and derigged precisely because they finish up in fields. Also at the end of the flying day at most clubs, personal gliders are put back in their trailers.
It's obviously sensible to get your rig checked by someone else who knows how to rig that particular glider.