I use depop for used clothes, reverb for used instruments and ebay for general items

Yeh, tons of stuff, and all of the above. I think the majority of the stuff I own(ed) was used, and a large portion of my clothing is secondhand.

I’ve bought an old guitar from a scammer. Well… not exactly a scammer but a very dishonest and tricksy salesman. I asked for a reasonably priced used guitar ready to be played on. He was able to close a deal by offering me a free 1 hr lesson. I show up to the lesson and he just blabbers on about his life and gives me a card to go see him at a club he plays in. And then tells me the strings on my guitar are old and need replacing and he’ll happily do it for free after I purchase the strings. I was so disgusted. I hate this type of shit.

Yeah I bought a guitar secondhand from somebody I knew, also some electronics I will buy refurb from newegg or Best Buy or wherever, depends on what it is

Yes. Online

I've bought a lot of used items from car to camera and secondhand store to shopping online.

No.

Yes, thrift stores (mostly clothes), yard/garage sales, flea markets, eBay, etc.