Having done both, renting through a broker and an individual, there's always risk. There's the "what-if's" that come up, such as... What if the owner gets their timeshare foreclosed on?
Broker sites have set prices, that adjust with each year. They pay their clients for their points, but have to charge a little more to you to make something for themselves. Going through an individual can be risky (most have references and such), but in the end, they're looking to put the points to use that they aren't using so it helps to pay for their investment (so most are going to help and stand by it) so you may wind up paying less than what a broker site would do. Just think of the broker site as a 3rd party to you dealing directly with a DVC member (cause that's what it is), they put your request out to their clients and if someone has the points to fill it, they enter your info in and get your reservation.
Also keep in mind that all the broker sites have different amounts of clients. David's may only have 100 people that sell points to him, whereas another broker may have 200. So each site is its own monster in what they have to work with to help set you up with a unit.
In 2014, we were able to plan a month out from our trip and one place we looked had nothing available, but we went to another broker and were able to get Saratoga Springs and AKL Kidani Savanna View for the time we were going. So keep that in mind as well.
As far as park tickets and such, the reason they take down all your info when booking is for the Disney reservation. It will come up in MDE under you. You'll get your magic bands and you can buy your tickets online at the Disney site and it'll all be linked right there in your MDE.
Just remember, nothing is ever guaranteed. As I said earlier, there's a ton of "what if's" out there, but talk with those who are renting the points and ask questions. It's few and far between (I believe) that DVC reservations through brokers or individuals fall through, but it can happen. Foreclosures would be the biggest one. As for someone saying about looking for rentals on EBay, I'd probably not go that route. There are a ton of options and avenues for booking DVC that are more reliable.