Personally I would never buy a used helmet. I want to know its history.
As for the Vic helmets I just bought one and found it to fit fine. I usually wear a medium and the Vic medium fits great. It also has a adjustable knob in the back that allows you to dial it in. Overall I've been very happy with it. I bought the Shortie helmet and I'm thinking about getting the 3/4 because of its price.
13 Vision Tour - PCV, Top Filter, Stage 1 Pipes, TW @ +4, Metz 888s
08 Vision Street Premium - VFC, Top Filter, Stage 1 Level 2 Pipes, E4s
Past Vic - 07 KP Tour - Stage 1, S&S Intake