Like presley, I bought a GPP unit on EBay. I had the contract/owner ID# from the seller before I purchased it and called GPP direct and found out exactly what I was buying beforehand. What I was buying for pennies on the dollar was a fixed week 2BR unit. The best units to buy, if you want to convert them to HGVC points is "fixed" week platinum units, not floating. Example, my 1BR is fixed and worth 6200 points, most floating units are worth 3400/4800 points in HGVC. My 2BR is worth 8400 points, most floating units are worth 5000/7000 points. Same maintenance fees, but more points for fixed and platinum week units. So I bought the 2BR on EBay. It was not a HGVC unit when purchased. But then, back when this was possible, I purchased a resale 1BR platinum (fixed) unit from the GPP resale dept. and part of the deal was to be able to convert both at the same time into HGVC, which I did, and have been quite pleased. I have the benefits of being a GPP owner and also the benes of a HGVC Elite points ownership. About the only downside I have seen for affiliate ownership is that you can only borrow points from one year in advance for the affiliates, not two years as with true HGVC units.
Best of luck in your purchase/decision.