Gumtree seems to be only scams these days and it's a shame. We've had the same stuff happen to us, even with a dog. I mean, what kind of person are you to lure people in with puppies?!
Though, that said, we did end up getting our dog off of a gumtree ad (granted from a junkie in Govan who got his dog together with his friend's dog to make some money), and we did get the house we're living in now off of there as well. You just have to be suspicious of pretty much everyone, unfortunately.
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It's not as bad for areas that are smaller, but for major cities and large towns you do have to be more careful.