I don't sale many, thankfully, I've never really been sure the best way to go about it, if I was waiting on someone I am likely to mess w/ the horse while I wait, may include lunging if I felt he needed it. And if they were in a hurry and felt he'd need to be longed before being rode, they may have desided there just wasn't time to wait and lunge if you were going to be able to ride at all. I really don't know, for me I like to be completely ready, have the horse up and groomed, and tacked, but apparently that is a red flag for many.
I can also understand not wanting to do a trial, w/ a very trusted friend maybe, but there are so many screw balls out there, I wouldn't want to hand my horse over to a stranger. (although I did agree to once, but when they came to pick him up, they desided to forget it and just buy him)
So if you like him, I'd see him again, only show up about 1/2 hour early, and try to plan for a day the owners don't have something else going on (so no rush).