I've recently had a scam approach when selling. I had a cheap English concertina that i wasnt using so i put it up for sale on Gumtree, Very quickly I had someone offering to buy it at the full asking price (around the £100 mark) from an African country. They said they were going to get their courier to collect it from me and wanted to know my bank details so they could transfer the money. Somehow this didnt seem to ring true. They hardly mentioned the concertina (i.e. its condition, tuning...) and it seemed an awful lot of trouble and expense to go to for what was a pretty cheap chinese concertina.
At the time there was a programme on Radio 4 telling how some scammers offer to buy and then send you an over payment by 'mistake' and ask you to refund the difference only to find that their original payment is then reclaimed somehow. I decided that this was what was going on and stopped responding to their emails. Maybe i lost out on a genuine sale but i dont think so. 'If it seems to good to be true, it probably is'