Over many years, I've rented many timeshare weeks that had been exchanges.
Was I fearful that something would go "wrong"? Never. Because I always (1) made sure the person had what he said he had (and the exchange confirmation was enough to establish that).
Then, after (2) payment (and I most often used something with insurance), I made sure he (3) changed his name on the reservation to my name on the reservation. And (4) called the resort to confirm that. By simply saying, "Joe Shmoe just a couple of days ago designated me as his guest. I just want to make sure I'm in your computer system so I will be able to check in without problems".
And the resort front desk has always without exception confirmed that I'm then on the reservation.
So what's the difference between me checking in and any one of the other owners checking in? No difference at all. Well. Maybe a slight difference if I was designated "RCI" or "II" rather than "home resort owner" as they might aggressively try to sell me a timeshare. But I always play Mr. Unnaturally Loud Talker and loudly ask something like, "I saw a 2 BR timeshare at this resort advertised on ebay for $1. Are you selling them for $1 too?"...and they quickly thank me and show me the door so as to not "disturb" their other potential sales (i.e., their other potential victimizations of naive innocents). And if they don't show me the door, then I'll follow up with a loud, incredulous, "The annual maintenance fee is THAT high!!!??? Are you kidding? Who would be interested in something like THAT???!!!" or some such objection. And hope that others hear me so that they may perhaps not be defrauded.
So let me respond to people who have said "that's illegal". I was a police officer for a time after I got out of the Marine Corps before getting some higher education and embarking on another career path. I don't recall a single part of the penal code that said anything like "renting a timeshare that had been exchanged via RCI or II".
Moreover, the resort could care less. It's an II or RCI rule. Not a resort rule. All the resort cares about is "is the person on the reservation?".
But what about RCI or II? If there's absolutely no way for them to know anything about whatever the rental deal was, if you're simply officially the "guest" of the person with the RCI or II reservation, how will they know any different? No way whatsoever.
So why would RCI or II even have such a stupid rule? The timeshare owner, having exchanged his owned high maintenance fee timeshare week plus having paid $289 (!!!) SHOULD (in my opinion) be able to do whatever he darn well pleases with it. But no. RCI won't allow the exchanger (for whom something came up and who won't be able to himself use the timeshare...like an elderly parent who died) to rent out the exchange for which he paid so much. The exchange company wants him to buy the right to return the timeshare into inventory (for an additional $89), even though he loses the entire $289 exchange fee. And then the exchange company will re-list it in order to double dip and get another $289.
So I understand the exchange company's motivation to stick it to the timeshare owner: pure greed. But I will always be on the side of the timeshare owner and not on the side of the (I would call crooked) big corporations.
Indeed, it's the exchange companies who make all the fraudulent timeshare sales possible. Their biggest and most effective argument sleazebag salespeople make are untrue claims about how wonderful the exchanges you'll be able to get. It's no wonder the exchange companies are owned by and in bed with timeshare resort networks.
So your rental will almost certainly go off without a hitch if you take reasonable "due diligence" precautions. Check in with complete confidence.
And quite frankly, you're in the driver's seat and can be very aggressive in your negotiations with the person renting his exchanged week so you can get a pretty sweet deal.