Why is it so hard to buy parts from people

At least with Facebook, I know marketplace is trash. I sold a motorcycle through marketplace. Potential buyers messages did NOT give me any notification the way a chat does.
I had to check manually. Sometimes I'd get some sort of notification from FB, but rarely.
Same after I'd respond: they would write back and there would be no way for me to know they responded if I didn't manually check. Really sucked.
FB also often edits out emails, phone numbers, etc automatically for "safety". I can post all kinds of terrorist propaganda there, but not the phone number that every Nigerian and "warranty center" calls at all hours of the day. Go figure.