I buy and sell a lot on Anibis, Ricardo and Tutti. I almost never had any issue in 15 years or more. When I had one, it was just small issues or misunderstanding that can be solve with the seller/buyer at worst with a refund. However I never used Facebook Marketplace as I don’t have Facebook. My wife did from time to time and said that many seller and buyer were rude, not replying, or ads were strange or poorly written. I guess it’s the platform popularity, or the fact that Facebook users are mostly using it from phone and doesn’t care to write properly, with details, as it’s more painful to do so from a phone.
You just have to use common sense, if the ads its written well or not. If the price/offer is too good to be true. How is the communication with the seller, is he coherent or not, does it have excuse not to allow in person exchange or avoid answer question? When one or more red flag rise, forget about it. And even if everything looks ok, when the amount is more than you can afford to loose, try to do only in person exchange or use second hand shops like Cash’n’Go, CashConverters (I did some not so bad deal there, even if it’s mostly over priced), you can also check Broki or similar.
I bought almost 4 year ago a phone second hand that I’m still using today, very happy with it. We meet at the train station, I tested the phone quickly. Paid. Then I did a full reset and install a different OS (LineageOS, I bought this model especially because it was compatible with this special privacy friendly Android custom OS).
I bought as well 3 tablets second hands (I don’t use 3, just one got the first stolen, the second smashed by an object that fall on it). For these I paid each time in advance and get delivered, each time in perfect conditions, almost like new, just one was a bit dirty but I could clean up like new with a special product for screen. They all worked perfectly, so much money saved.
Another funny, purchase I made from an online ads, was a graphic card, a long time ago when it was not on shortage like now. The guy show up at my work place as he was close by, and we trade on the street from his trunk. He was an independent mounting PC for his customer and got the wrong card for one and had to paid to return it. It was new and he made a receipt for it from his company. It worked for 6 years then I sold it on Ricardo for a quarter for the original price I bought it.
So it’s a matter of common sense, communication, trust and a bit of luck I guess.
If I might, little ads for my blog, I wrote an article about selling stuff online in Switzerland: I made 1000CHF by selling secondhand stuff – ELUC
I should maybe write one about buying as well.