I had the very same experience during the past week. I posted an ad for my TV on Gumtree and got a text from someone called Julia Fletcher asking me to reply via e-mail. I did and she was offering the full price for my TV, said she was disabled and in a wheelchair but would arrange for her own courier to pick it up.
I then got an e-mail saying the courier company wanted the money up front, via moneygram. She said that she would put the full amount for the TV, plus the £200 courier fee plus another £40 for sending the moneygram to an address in Cyprus!
Then came an e-mail, supposedly from PayPal which said there was money waiting to be put into my account pending me sending the moneygram. By this time a million bells were ringing so I called PayPal who were great! The woman did not have a PayPal account and it was definitely and obviously a scam!
If in doubt call PayPal as it is free and if you don't have a PayPal account it is always a scam!!