Long time swappa user here. The site is definitely not what it once was and I find myself looking elsewhere first when trying to sell.
It used to be mostly individuals selling their phones but now it's overrun by resellers and eshops like eBay is, as well as lowballers and foreign buyers asking to ship internationally. But I guess when anything grows too big, that's what happens.
Paypal didn't help when they changed their buyer protection policy to 6 months a couple years ago. Now a sleazy buyer can use the phone for half a year, then claim there's a problem and demand a refund. They won't necessarily be successful, but it's not a fight I want to have when phones are pushing $1000s nowadays.