Gumtree scams - especially where they offer to pay more - or where they are 'working on' [insert any remote place here] and can't contact you easily and someone else will collect the goods are RIFE!
Do a Google 'gumtree scams' and you will be amazed.
I wouldn't even respond to anyone who can't personally turn up to view and pay CASH - folding notes - otherwise I would be very rude to them!
Remember the old adage: "If it seems too good to be true - then it is!"