I like the single goalie ones MUCH better -- and had a table similar to that one when I was growing up. The corners are all sloped -- and I got pretty good with a touch-shot with one of the corner-forwards that used the bank on the slope to slip the ball in the goal behind the goalie. I remember every time I'd make that shot I would laugh hysterically...
The main thing to look for is if all the bars are straight and if the table has any damage that would make it unstable and eventually fall apart.
Try moving the bars around and back'n'forth aggressively -- as that's what you'll do while really playing. Does the table move around? Like it's too light-weight? The heavier the better, especially if you're older than 12.
If you've got a game store near you -- like one that specializes in pool tables, drop by and get an idea of what replacement parts they have for foos ball tables. Chances are, if there is a broken man on the one you're buying, it's easily replaced. The only hassle is FINDING the part.
edit: Oh, and take some furniture polish, like Pledge, and a rag. If the table has been sitting for awhile, the bars are probably dirty and won't move nicely. Wipe them with some Pledge, and they should move and spin effortlessly.