You can always fill it up in his garage, so if it doesn't hold, at least it's his mess.:lol2: Personally, I would water test any tank from someone, unless it's still crated. I would especially do it on a "used" tank sitting around that has never had water in it. Let's face it, if you buy a new tank, who knows how it was stored, unheated warehouse, back of LFS since 1988? But, at least when you get it home, if it does leak, you have some recourse. On a used tank, even if never actually used, you get it home, find a leak and you're probably SOL.
It will probably be fine. Just take a half hour and fill it up, check it, and dump the water.
When I first caught your thread title, I thought you were looking for someone to house sit your tank while on vacation!:lol_large
Hope it works out.
Henry