Open box is a gamble, but having bought a lot of them myself, the odds of getting a good card are better than 2:1. In other words even if you got a bad one and had to pay $8 to return it to them, then bought another (open box), odds are you still save money over buying a new one.
IMO, the larger gamble is whether it is the right time to spend $100 on an AGP video card. If you have DDR1 memory you can reuse, that $100 would get you a skt 939 CPU and refub'd motherboard with a little $ left over (depending on what you get), and if you sold your present CPU & board you'd come close to covering the lower price of the PCI Express version of a 7600GS or whatever. That may not be the right choice for you, but in retrospect I always felt I got a better value out of begining an investment in a newer platform tech than trying to squeeze another year or two out of an older tech.
Plus if on a limited budget, it could be even more of an expense later to have to buy motherboard, CPU, video, and possibly memory too all at the same time for the next upgrade.