For about five bucks you can get a checking pen. I sold a truck recently for cash to an out-of-town buyer who did a fly-in drive home. I made sure that I had all of his contact info, Google his home address, etc before he showed up.. I bought the pen. I didn't want to check the money right in front of him, but as soon as he left I did. I figured if there was counterfeit the cops could still catch up with him while he was on his way home.