Controversial as it may be (wot me???
Perhaps the most common lie we hear is "I've only got xxxxx can I have it for that please?" when in actual fact the customer has more money available.
Another great scam, which I fell for recently, involves children. To quote a dealer this morning who pointed it out to me "they train their children well!" Oh yes! We get young children approach us, clutching a 50p in their hot and sticky little hand, claiming ignorance of coins but stating that they are studying such and such at school. Feeling sorry for them the mug, er I mean dealer, sells a coin at far below the price he should, thinking he is doing an innocent youngster a favour. Ha! More fool the dealer! That innocent youngster just suckered him into parting with something for a damn good price which is now on another dealer's stall, or in the hands of an amateur eBayer.
Of course, then there is the distraction theft. Engage the dealer in conversation about a coin, while your associate pockets what he wants.
So, the next time a dealer eyes you with suspicion or is reluctant to stand and chat, it may not be the colour of your skin, your accent or your choice of attire that alert him, it may be that like me he has been cheated so many times he is now cynical.
Incidentally, we have to factor in losses from theft into our prices, so these activities push prices up for all customers - just like cash-for-crash car accidents push up insurance premiums for everyone.
Matt