I do a lot of cash deals.  Usually have $1000 in my wallet just in case I find a deal.  It helps being 6'3" and intimidating looking.  If I do a deal on craigslist I show up with a gun on me or at least one in the pickup.  Usually scams are easy to spot.  Immoral people that think they can take what is not there's not so much until you meet them.  I'm sure I've done some deals that the plan went from "we are gonna jump this guy", to "Oh **** he is a big MF".