Why would more sellers back out of Fedelity contracts compared to others?
Fidelity has a business arrangement with DVC. When DVC owners want to sell and contact DVC (usually to ask if DVC will buy their contract back, which they won't) they are referred to Fidelity in exchange for a cut of the commission on the referral. Because of that, most of the "distressed" DVC resales (people who HAVE to get out of their DVC holdings) end up in Fidelity's listings.
At this point, the seller is making a difficult decision to get rid of something they like because, for whatever reason, they just can't afford to keep it. Many times, the reason they can't keep the contract is they bought direct at a very high price, financed, and now their contract is worth MUCH less than they paid (and much less than they owe). But, their focus is getting rid of the DVC contract and they're really not thinking much further than that.
A deal is reached -- say 200 points @ $50 per point = $10,000. Seller says, "Whoopee, at least we sold it!"
Once the offer, acceptance, and deposit are in place, the deal goes to ROFR. If it passes, the transaction goes to the closing company.
At that point -- for the first time, really -- the buyer is given the details of the transaction in REAL dollars and cents. It's called a "Good Faith Estimate," or something like that. It shows the selling price, all costs owed by the seller, and the seller's NET proceeds from the sale.
When the seller reads it, it looks like this (I made these numbers up):
200 points @ $50 = $10,000
less 10% commission of $1,000
less misc selling costs of $150
less LOAN PAYOFF OF $17,305
NET: You
OWE $8,455, which you must PAY AT CLOSING!!!
Seller can't pay the 8 grand and bails out.
That's simplified and the numbers are fictitious, but you get the general idea -- the seller finds out the resale price is so much less than they paid that they CAN'T sell.
This problem can occur with any broker, of course. But it tends to occur much more frequently with Fidelity because DVC is referring mostly problematic contracts to them.
Where are you looking to purchase, if you don't mind me asking. I have been doing way to much research lately and would offer any help, if you need it. 
