Water damage under shower.

Sounds like you have some loose compression fittings in the drain line plumbing, pretty typical. I don't thing the Amish craftsmen know how to tighten fittings up. Had the same deal with my new one but I checked all of them before I ever used it. They were all either loose or had inadequate blocking under them or both.

Very typical, what I never buy used, only new but I go over everything before using the first time, I dislike surprises.