Leigh,
I think you have the right to be worried. I don't think you'll have a problem with your reservation, but when you deal across the internet with someone for a substantial amount of money, extra steps do need to be taken to insure your comfort.
You had those steps in place, but they were not followed by the seller.
Communication is the key, and you were let down. And that's not your fault.
I've rented points, scanned confirmation letters and sent them as the only form of confirmation. If someone wants the actual hard copy from Disney, I send that also. But at the very least, email and phone numbers are a must.
Closer to the time of the reservation, I always check to make sure the reservation is still intact, and then email/telephone the renter to let them know everything is ok, that a computer crash hasn't bumped their plans out of the system (there has never been a problem).
I always recontact the renters after their stay, to see how they enjoyed the trip/accomodations. I have even called them at the resort, to make sure everything went smoothly at check in (and it always has).
Several times, we have been recontacted before we had a chance to contact them first. One family even sent a very cute card to us while they were still at WDW (thanks BSB, my daughter loves the card, keeps it in her room!).
The renter should have done more to make sure you were comfortable with the proceedings.
Best of luck Leigh.