Gumtree is full of both bargains and scammers
I once bought a nice guitar off eBay, something I’d been on the lookout for a while on Gumtree as well. The day after the auction ended, I was alerted to a new Gumtree ad. The exact same ad had been copied, photos and all, with the price half what I paid. I was sure mine was legit, so I responded to the ad to see what would happen. I got a long message back with an email address which all seemed fairly genuine, not your average Nigerian nonsense. Quick Google found several others had been caught out and transferred money in good faith.
At the same time I’ve had some great finds on Gumtree but I stay local only. And I tend not to give my phone number or address until I’m sure they are not a psycho hose beast.