Ron,
It was extra rewarding as the guy tried to sell off some booklets I had put down on his table when paying.
I forgot the booklets, a 1950s RWS catalogue signed (and formerly owned) by Henk Visser and an early Mauser Parabellum manual and walked away.
Found I had forgottem them and upon return I found he had placed both items for sale on his stand....
I picked up both items in front of a customer and told him I wasn't too pleased with his behaviour. That worked