If this is a someone you know personally, I would have no hesitation to try to buy it without a broker. The broker serves to facilitate the process and see to it that the sale proceeds with all components in place. For a private sale, you (and the seller) will need to handle those details yourselves.
IMO, there is no advantage for the buyer in a private sale of a DVC purchase because of Disney's ROFR. If there would be a considerable savings for the buyer, then the private sale would be a win-win situation in spite of the additional legwork involved- but since ROFR will determine the actual price, using a broker eliminates the pitfalls without any additional cost to the buyer. It may save the seller a few $$ , but there is no real benefit for the buyer.