My regs are strongly encouraged to bring new players. My rule of thumb is, "If they're welcome in your house, they're welcome in mine, but their behavior reflects on you." Stakes are low, and I've been playing with most of these guys for many years, so their endorsement is good enough for me.
I've also invited unknowns from 2+2, CT and PCF, and I've never had a single problem with any of them. In those cases, I usually ask for a full name, cell number and email address.
I've only had problems with two players. One was a guy who thought that being an asshole at the table was "just part of the game," and the other was a guy who got caught cheating the first time he played with us. I was the one who invited the cheat, and I banned myself for several weeks for that idiocy.