Can I get scammed this way?

[.Lethal]

I can only assume you have very limited experience with it, as using it in these sort of circumstances is entirely the point of it.

Personally I've paid via PayPal whilst using Gumtree quite a few years ago, but never had any problems. I've had to use PayPal CS probably 3 times in 15 or so years, without problem (none related to Gumtree). So quite limited indeed.