If someone rings our bell we try to give(some impatient collectors don’t give you a chance to get to the door). And acquaintance of mine told me one never knows who Eliyahu Hanavi is.
About the teudas,one should check the date and also look if it is real,in other words that the date or name doesn’t look like it has white out and corrections. I was once at Copy Corner and there was someone photocopying,whiting out and putting in corrections/changes.
One who insists on coming into the house, is allowed in and my husband will gladly listen to his/her story.
At one point there was a certain man who would ring our bell close to Shabbos. Each time he had another story(and often another type of hat) and yet i would give him no more than a dollar. Once he came about a week or two later than a previous visit and his story contradicted what he told me earlier. I nicely told him and also added that his stories were so good that if he would publish them he would make more money than ringing peoples door bells. We never saw him again!
If he would again ring my bell, he would probably get his dollar no more or less!!