While travelling I mostly use booking.com, but they're going downhill. Their reviews are more realistic then Airbnb and I got good discount because I've used them a lot. Long time stays, well, talking to others or renting on booking/airbnb for a few days and then talk to the owner. In Mexico I've also rented just from a paper sign behind the window of a family house. It's quite common and fun to do it like that. Never had any issues.