It may take a little longer to close. It may not, but not all sellers are motivated to sign and express back the paperwork promptly.
Remember (as has been mentioned) to factor in closing costs.
Sometimes sellers back out (Disney never does - well, as long as you pass the credit check).
You don't get to take advantages of promos (a backpack, free nights, or whatever the current promos are) buying resale.
If you want a relationship with a
DVC sales guide, you are going to have to establish one after the fact with someone who will only get possible commissions from your add ons.
In addition to buying a contract with all the points borrowed, you may end up with a contract with lots of banked points that won't fit into your vacation plans. Not a huge problem, you can let them expire, rent them, or give them away - but know what you are getting and when you are getting it and when you have to use it by.
Because of the borrow/bank points issue, the possible lengthy closing and the possibility of backing out, don't buy a resale for a vacation that you have your heart set on less than about ten months out (and a year even more would be way better - with the flexibility of going earlier if you want - or not having vacation plans at all). It would be frustrating to have a seller back out after spending six weeks on a deal, the next deal having a slow closing, then getting a contract where you need to spend all the points in six weeks-- and then discovering that there isn't any availability when you want to go next month anyway!