I won an eBay auction from them in April for a Buganvilias Presidential Sky Suites contract. It took about 6 weeks for the contract transfer to take place; that was dealt with by the resort only since it was just an RTU contract. In the end, all I got from them was an e-mail saying that the transfer was complete; I believe that they got the letter reporting the completion but didn't provide me a copy since it had the seller's contact information. I eventually requested a confirmation letter directly from the resort and got it in about a month.
Of note, the contract they provided showed the "closing costs" to be about equal to what I paid on eBay for the contract. The resort itself charges about $150, I believe, to transfer a contract. I have no doubt that they pocketed the balance, so I would never attempt to sell a timeshare through them. I suspect that they or another group got an upfront fee from the sellers as well, but never inquired about that. (Not really sure why anyone would use a resale company to get out of a Mexican RTU contract anyway.) If they were selling another contract like that on eBay that I wanted, I would probably go ahead with purchasing from them, but there's not much incentive for them to work hard on a transfer since they already have the money.