So, I'm a bit of a risk taker, if I buy a resale for more points than I can really use, what should my confidence level be for renting the excess -- 80%?
IMO, if you are willing to do the work (and price your points with or slightly under the market), you will virtually always be able to rent your points. That's especially true if you can offer points more than 7 months in advance for one of the smaller, near-park resorts during the home resort booking priority period. (Those resorts would include BCV, BWV, BLT, VGF, VGC, Poly & VWL after the construction is complete).
Keep in mind that you will be competing with the brokers (who offer escrow service) as well as many owners with established renting track records and repeat customers.
Some things to think about:
You will be responsible for any bills / damage your guests may leave behind. Disney is not great about trying to resolve those issues - it's easier to just freeze your account. To be fair, this is very rare - we've only read about 1 or 2 such incidents here on the DIS.
Most of the brokers have point minimums for owners who want to use them to offer their points.
You are allowed one transfer (of points to or from another member) per use year per membership. That's one into your account or one out of it, but not both in the same use year. There is no limit to reservations that you make for others. However, it is believed that making more than 20 reservations for others will trigger an audit to see if you are in violation of the "commercial" renting provision. Commercial renting is not permitted.
You may encounter some "high maintenance" customers (be prepared to do some hand-holding and perform TA functions). You will also encounter some who are just looking for rock bottom prices and may cancel out on you if they find a better deal. You can include deposits and non-refundable provisions in your contract to minimize that. However, owners do compete on terms, so you need to balance those things with the difficulty of finding customers.
You will need to develop a written contract and policies and figure out how you will accept payment. Payments present their own set of risks.
You will need to figure out how to get customers. If you plan to use the DIS R/T Board, you will need to pay a fee or meet the posting requirements. There is a Sticky Thread at the top of the R/T Board that explains in detail. Beyond that, you'll need to establish some some of reputation/ references so that potential customers will feel good about renting from you. Posting here is a good way to start doing that. Trust is a large component of
DVC rentals.
My BEST advice is to not to buy more points than you can comfortably handle on your own (financially) should renting prove unsuccessful in any given year.
Good luck!