I think its very nice to greet meshulachim with a smile. For the genuine ones who have to lower themselves to knocking on peoples doors and asking for money being greeted with a smile means so much. And if they are really in need of money theyll be happy with whatever you give them. But inviting them into you house is not always the right thing to do. I would always offer them a drink or something until the one horrible incident. One meshulach marched himself in and demanded a meal. I was very uncomfortable and i was home alone. He stayed way longer than he shouldve and acted very inappropriately. It was very close to shabbos and he asked a neighbor if he could stay for shabbos. In shul a few people recognized him as a known child molester from out of town. The Rosh Yeshiva paskened that even though it was shabbos he has to leave yeshiva lane right then. After that the Rabbanim got together & anyone collecting in that community had to have a dated paper signed by them. They would look into them and make sure they were genuine. Anyone that didnt have one we shouldnt let them in or give them anything.
