I got lucky as well, buuuuuttt, there were a few things in my favor. I got my truck from MCAS Cherry Point here in North Carolina and I also happen to work on Cherry Point and had our manager take a quick look at the truck when he made a DRMO trip to dump some hazmat stuff. Also, GL is required to display pictures of each truck they sell, I heard they got in trouble for not doing that a while back and were fined heavily. The descriptions are usually close, but look at the pictures very close. If stuff it rusty or it's been sitting with no air cleaner on it, then count on it to have not been running for a while. If, in the picture, you can't make out the fins on the alternator, that means it's probably running. The only thing I noticed in the pictures of my truck was a catch pan under the front of it....turns out the radiator cap was bad and it leaked some anti-freeze
I had the numbers run on my truck to figure out where it came from and it if saw a rough life, luckily it didn't. I also got lucky that the rear driveshaft wasn't bent, I actually sold it a few months ago after I did the motor swap.
When I finally went to pick my truck up, I borrowed a previous employer and his F550 with trailer in tow. I also took a multi-meter and two fresh batteries and figured if that couldn't get it started then I'd push/pull it on the trailer. Luckily, just the rear battery was dead so I swapped it out and drove it on the trailer.
Hope yours turns out as good as mine did!