If you really want to frustrate new shooters, give them anything with a full choke. To add to what rc said, more game is injured because of too tight of a choke than too open. Other than turkeys or maybe varmints, I can't think of a reason to go with a full choke.
And as 243wxb said, pattern it first. One of my favorite guns growing up was my grandpa's 12 gauge (I think it was a Model 12) marked as full choke, but it patterned like a light modified choke. He would never give us a straight answer but I'm pretty sure that he had it opened up after he bought it.
If it is definitely giving full patterns, send it to Carlsons for tubes. I haven't had anything done by them, but I know several people who have and they've been very happy with the service.
ETA: Also, prior to the introduction of modern wads and the prevalence of softer shot, a full choked gun would shoot a much larger pattern than the same gun with a modern wad and hard shot.
Matt