My most memorable scammer was one I had a few years back. I'm in the UK, and at the time (still now, although it's not as bad) there was a a problem with various gs and electricty companies 'switching' customers without their knowledge. The salesperson would call, ask about your gas / electricity bills and, under the guise of getting details in order to be able to send you offers, or details of how they would be a far better supplier, would get enough details to switch you to their company.
I had been doing some research and had decided to switch my supplier, to get my gas & electricty from one provider (many do a 'dual fuel' discount, so it is cheaper than having one gas and one electricty supplier). I'd decided which company, and which tarif, I wanted, but I hadn't got around to calling them to set up the switch. At the time, I was getting door-to-door salesmen several times a week, so I wasn't particularly surprised to open the door one evening to find a salesman from the company I'd already decided to switch to. I decided (after checking his ID) to let him in to hear what he had to say.
He took details of my enregy usage and told me that he would be able to get my costs lower (which I already knew) but didn't realise I could see that the numbers he was entering into his computer were lower than the ones I was giving him, so the result would be artificially low.
He then went into his speil about needing my details to let me have the full details and comparisons, and specifically told me that he was NOT switching me. I noticed how he had set up his clipboard so the clip covered the words ' contract for supply'. I signed, however, as I had already decided to go with this company on this tarif, before he ever knocked on the door.
At which point, as he got up to go, he asked me, chattily, what I did for a living. "I'm a lawyer" I explained "That's why I read what I signed" The conversation then went like this:
"Er, perhaps there are one or two things I should mention"
Me: "Is one of them the fact you just got me to sign a contract, while telling me explicitly it wasn't a contract, and was for information only?"
Him : "Um. yes"
Me " And perhaps another was the bit about how the figures you gave me wen't based on the consumption details I gave you"
Him "Er, yes, that too"
Me: "Anything Else"
Him "um. no"
(Yes, I did call both the company, and local trading standards. Since I had the copy of the contract I had, and was able to give them, all his details. I received a fulsome apology from the company, and they agreed to honour the (unrealistically low) figures he's given me, for the first year of my contract. I don't know whether he was fired or not, although I'm fairly sure that at that time it was something which all of the energy companies were actively encouraging their salesmen to do)
It made me better realize how people are caught out. I was 99% sure before he started that he was going to try to switch me, AND I have always been very cautious about signing anything, but he was VERY convincing .