i have a pen that detects counterfeit money. on the end is a UV light that shows the internal strip also.
basically the way i conduct my sales on craigslist is this:
1) agree to meet at a Starbucks, Panera, or Apple Store
2) place item on the table and hold onto the item
3) request that buyer takes out cash, counts it on the table and uses my pen on the money to verify it is authentic
4) slide item to buyer so he can open it up and inspect it while i then take back the pen and verify the strips and other markings with the UV light
the reason why i do this is because a while back a buy tried to break the seal and open up a brand new ipad that i was flipping without showing me the cash. something seemed odd, so i asked to see the money. he said "I GOT THE MONEY". i said i want to see the money. he said he has it, not to worry. i take the ipad back and i say show it to me and count it. he counted it and he was $75 short.
he was hoping to have been able to score the iPad for $75 less and since he opened it, he was figuring i would just agree to the sale. yeah, nice try