I like him. If he's quiet, been out and about, that's what you want. Doesn't matter whether he's done official or assoc. dressage, as long as he's been out and coped with it!!!
Who cares if he's not spectacular looking, that's not what you need right now unless you want to go and do official showing which I don't think is up your alley???
Go have a look with an open mind ;) Don't go in there thinking "I'm going to buy him" or you'll end up in the same situation. But I think youre already aware of that :)
Be aware though that these days very few people will offer a trail period. Too many things can go wrong, what if the horse injures itself or has to be put down? Who pays the bills and do you still have to pay the full price for the horse since the owner has made a loss by sending it to you?? Those are big issues and the reason why few will send a horse on trail.
By all means ask about it, but if they're not happy, you will want to at least be able to take him out to your instructors, put him under some pressure there and see how he goes in with other horses. Also ask if you can come up a few times to ride him before you commit to buy.