That fork was bent backward in some accident. (Running into a wall at speed?) The top of fork blades should follow a projection of a line drawn axially through the center of the head tube so these forks are pushed backward probably at least 6" at the front axle. Any impact feeds through the entire bike so it is possible that there is other damage to the frame although it is not readily apparent in the photo so it may be OK. The fork can be fixed but for safety's sake, if nothing else, I would be inclined to replace it. I think the tank is worth around $100 if there are no major rust issues so I would go from there considering what the bike is worth in the grand scheme of things (ballpark $100-$175 but if you like it maybe up to the asking price for the whole lot is not the end of the world) and how that price sets against the backdrop of your desire to own it. At the price he is asking for the lot, you could probably buy all eleven and sell the other ten either making a bit of profit or at least getting the one you want for next to nothing.
