Yes it's water damage. Yes, the owner is FOS. Nobody cleans the floor of an RV like they are swabbing the decks of a commercial kitchen, giant rag mop flying about, and a pail full of suds on wheels, with the built in wringer. I have bought several used RVs in the last two decades, and looked at hundreds of others. For me it's real simple, if I even think that it may have water damage, I move on. No rationalizations in my mind that it's "no big deal", no good story from the owner, no salesman telling me that's it's "just cosmetic" no nothing, walk away.
An owner of a repair shop gave me this advice, years ago. He said leaks are like icebergs, you only see a tiny bit on the surface, the real damage is hidden, and it's often huge and ugly. He told me that he occasionally gets a client who asks him to fix "a tiny leak at the shower skylight", or another harmless looking stain from a "small" leak. Once he starts digging, the tiny leak has gone on for years, the bathroom wall is moldy mush, and the floor behind the shower is starting to rot.
