a) theres a whole wanted forum over there
b) never buy a second hand helmet, for all you know it’s spent several times it’s usable life sat on the parcel shelf in the sunshine, inbetween being used as a battering ram.
c) fit’s a personal thing, even between models in the same brand there can be variations (I like some 661’s, others in the same XL size I can’t even get my head in the opening!)
You can get half decent FF’s for £40 new, not worth the risk.
^ This. My full face has only been worn 3 times and looks as new but I had a horrendous smash a few months back and I wouldn’t wanna sell it to someone and put them at risk. 661 comp shifted is about £60 brand new and a nice looking helmet.