Post your requirements stating only direct owners ,no agents. Check the house book matching with the owner Thai id. Make payment using bank transfer and not cash. Make sure the bank account matches with the owner. Have a rental contract draft up.
They do border run because they have max out the extension 90 days, so they have to exit out of Thailand and then re enter again. Instead of getting a proper visa, they abuse the immigration system by doing border run which at a point of time they get rejected.