"Hello, this is Evangelist..." : Do you let them come preach?

I confess that I saw a thread similar to this on another forum and thought I'd like to see the responses to the question from some of the AFF crowd.

Every Pastor I know has, at some time or another, had a telephone ring only to answer it and hear, "Hello! I know you may not know me but I'm Evangelist (Insert name here) and I just wanted you to know that I'm in the area with some time off and wanted to know if I could come preach for you while I'm in the area?"

QUESTION: Do you let them come or do you generally turn them down?

QUESTION: What is your philosophy of dealing with those calling wanting to preach for you?

QUESTION: Have you ever been 'burned' by someone and wished you hadn't let them come?

This ought to be interesting and I'll hold my viewpoints for a little while to see what others think...

Let's hear your answers!