I can't comment on the brand as it is probably a European variety; however, what you want to look for is primarily a good fit. You want a suit that fits snugly, but is not overly tight or restrictive to your range of movement. The goal of a wetsuit, despite the name, is to keep as much water away from your skin as possible. Therefore it is imperative that there is not a lot of space between the suit and any area of your body. The way that it seals at the neck, the wrists, and the ankles is also extremely important as well; if those areas do not seal tightly against you you might as well not be wearing a wetsuit at all because you will have a constant flow of water cycling through the suit.
An additional concern with buying a used suit, beyond the usual hygienic issues, is the durability of the neoprene. After repeated exposure to pressure at depth the tiny air-bubbles that make up the material begin to degrade over time. This means that an older, well-used suit will not be as effective when it comes to providing you with insulating warmth. If you are going to buy this suit make sure that it still has plenty of useful life left in it. When you examine it the neoprene should appear thick and be springy when you pinch it between your fingers. If there isn't much rebound when you let go of it chances are that it isn't worth buying.
My advice would be to ask the seller plenty of questions such as how many dives has it been on, how deep, and what did he do to maintain it (for starters). If it is an older suit that has seen better days you will be better off buying new because you will be replacing it soon anyway (or you'll be miserable and give up on diving altogether).