bits of this have been mentioned elsewhere, but i think the concept deserves to be pulled out as its own specialist scam.
Essentially this scam relies on a couple of human traits .
If someone has made a considered decision to trust another player, or make a decision based on analysis etc, they are actually quite vulnerable.
If their decision proves to be wrong their mind is far more willing to accept that they are still correct.
what does that mean ? Well you scam someone, initially they cant believe it, then they have doubts, maybe get angry etc.
when they are in that staste of mind you can say - sorry it was a joke, no you havent been ripped off, I have just got to do xyz before I can complete the transaction, **** i have connection problems, etc etc etc.
It is far easier for them to believe you havent ripped them off or they have not made an error of judgement.
when the "customer" is in this state of mind - go for the double whammy.
The uyare weak- they will make judgements that are also weak or snap (in many cases) and this means u can gouge them for more $$.
Sorry here is your item, heres your gold back (send it cod), gwet someone else to message them to offer help to get item back etc etc (just use your imagination and trial and error)whatever to get some more cash out of them or set them up for another scam over the short, medium or long term.
what is an interesting component of mmog is that a lot of relationships and friendships evolve from conflict situations - from the simple insult that leads to conversation and later friendship to duels, trades etc etc - turn a scammed customer into a friend and scam them again a few months later.
The double whammty is great when it works. remember you might as well scam 1000g as 1g - they often involve the same amount of work.