Wow. No offense, but I think this is just bad advice in itself. I understand your point and context, that if you are unable to trust a renter, then you shouldn't be renting. And true, sometimes walking away from something is justified, warranted, and the best thing to do. But I think its terrible advice to just walk away from something just because you are uncomfortable and there may be some effort involved to make something work. Some of the best moments in life come from unknown and uncomfortable situations where you had to take a risk or leap of faith. Always playing it safe and running away anytime something isn't working out would lead to a pretty boring life.
In this case, I think the OP did a lot of great research and work, enough to be pretty comfortable with the transaction. The reservation not showing up on the website understandably raised an eyebrow, but if they had just walked away, they would have missed out on a great opportunity since it turned out that it was just a error on the name. Other than a posting history, this renter (and rentee) has done everything right.
When I rent, I too am quite anal about being comfortable with the renter, doing all the things, and a few more, that the OP did. IMHO, if you can confirm that a person is an owner, can verify the personal information they give you, can agree on terms and a contract, get a copy of the confirmation, and finally (and probably most importantly) get a good vibe from the person, its probably enough. If a potential renter if forthcoming with all this information, and you can confirm it all, it is very unlikely they are trying to con you. Checking post history is great and can often seal the deal, but low post counts don't mean that they are just lurking swindlers. A lot of people just use DIS to rent out their points in a pinch, and aren't frequent renters or Disney fanatics like the rest of us (and that's OK). Out of the 6 years I've been on DIS (and the 4 previous I had lurked), and the thousands of rentals that must have been facilitated through DIS, I can only remember a small handful of rentals gone awry.