the problem with id ect. is if the person is a crook they may have stole the wallet or purse and then had the front to got to the owners house and called you. there realy is no sure fire way to tell ( i have knocked a neibuors house before to ask ) a disclaimer is also not a fool proof way either so you just have to trust your own instinct sometimes, ask questions like whats in the cuboard in the hall (you have looed through the letter box and knocked it to see if there is any one in and to see if rex the boxer dog isnt going to take a chunk out of you
) but if you are not happy then a call to the local police is nesasary. if you called them to every opening they will soon get pissed off with you.