I have experience, I hate to admit. Though it is a bit dated, I think it is still valid. My wife and I were warmed before we got on the plane to Cabo back in 1996 and the cabin crew on the plane warned us before we landed in Cabo. We arrived fully armed and prepared to ward off any and all attempts to get us to buy, or so we thought. All I can say is - they are very good at what they do!
After three years of ownership, the purchase plus maintenance totaled approx US$11,500. We could see the writing on the wall that it was a bad purchase and sold it through a resell company for US$1500. I now consider that as a $10,000 education course from the school of hard knocks.
ThomasBeyer is right - no one forces you to buy. But rather than defaulting and possibly setting themselves up for trouble down the road should they decide to purchase other property in the US, I would strongly recommend your friends swallow the bitter pill, put it through a resell company and take whatever they get to go buy a hang-over so as to speed moving on. They come away with a clean record and at least a few dollars in their pocket.
To finish the story, we signed the papers to purchase on day three of seven of our holiday. Buy remorse hit me within hours, totally ruining the remainder of our holiday. We purchased on our Canadian visa card, so walking away from it was never an option. We never did returned to Cabo. Our purchased week ran Wed to Tues, perfectly matching our flights that year, but the following year, the cheap flight down arrived/departed on Fridays! Never thought about that before buying.
Good luck to your friends. They have my sympathy.