I once tried to sell something on gumtree and within 10 mins I had 2 people saying they would pay full price but needed it shipping to America and I would need to pay the courier £100 directly and they would reimburse me...
I find gumtree a brilliant way to invite people to quiz you about things you no longer want.
In any advert, start by saying "if you can see this ad, it is still for sale". I guarantee you will be asked, despite this, if it is still for sale... Also, answer within seconds... and there will be no further questions!
Infuriating, but at least it isn't
eBay.