I'm gonna meet a guy that's selling some used m43 equipment. Housing (EM-1) and lens is about 1 year old, with warranty. Is there a checklist you guys got when you buy used? The only things I'm certain I'll check is: Front and rear glass on the lens. The "frame" in the house (no scratches/damage). (Don't remember The English word). That they work combined. What more is important?