Second hand buying tips

[Tara]

I'm thinking about buying a second hand Mamiya RB 6x7. I've been told about one for sale for a very good price. My friend has bought accessories from the same guy and says he seems trustworthy. My friend has also looked at the camera I am thinking of buying and says it's in mint condition. The price seems really quite low. What checks can I make to put my mind at rest if I go and see the camera? What should I look for?
I"m probably just being overly cautious.