Suggestions on checking up
Last year I bought another Marriott (Desert Springs II). I called up owner services and explained that I was buying and I gave them the unit ID number (in my case it was a number along the lines of DS*9876*15*B (this isn't the real number). The "15" was the week number (for recording purposes - - but it confirmed to me that it was a "gold" week). "B" signified (IIRC) "Both" years rather than an even year or an odd year. "DS" stood for Desert Springs. The people at the other end of the phone were pretty cooperative and confirmed to me that it was the season that it was represented to be, an annual, and a lockoff.
On Tug, I read advice about Estoppel. Apparently an owner can request an Estoppel letter which identifies the unit, liens, etc. I recall from reading on TUG also that if you have the seller and buyer on the phone with Marriott Owner services that you might get reasonable info over the phone.
I didn't research my unit with a lot of scrutiny because I was buying on eBay from a seller who had sold TONS of TS and had a near perfect rating. But if I was buying from someone with only a few TS sales (check this), then I would have been more concerned. I was only paying a few hundred bucks and my strategy was that if it turned out to be something other than advertised that I was going raise "Holy H..." and make them refund my $. But it was a good seller and that wasn't necessary.
I suspect that there are LOTS of other people out there that have more insight than I do and who will offer additional or different advice.