Mate i was in your position last week selling my MK5 GTI, the only acceptable methods of payement are:
Bankers draft ( but pay this into your bank before you hand over the keys, the bank will know straight away if its a forgery, and can tell you if you can draw funds against it immediatley
Cash: cash is king, but again do the transaction in a bank, pay it in before you hand over the keys, that way the bank will spot genuine fakes etc, and once its in, theres no comebacks ( this is how i sold mine for 10K ) but phone your bank and ask if cash is okay because of money laundering laws, and bring ID with you.
Telephone transfer: can take from one hour to 3 days, check with your bank, they will tell you how long it takes to clear.
Cheque: if the guy insists on paying by cheque - he gets the car 6 working days later when the cheque has cleared.
Best places to advertise i found were autotrader ( still the most viewed ) and pistonheads ( got alot of enquiries via site )
I was also nervous about it, and was sure i was being scammed, but it was genuine, and i sold my car successfully, good luck.