I tell the truth.
Every time I've done that I've been ripped off. So now you have made me extremely nervous and that's not a good start. And it makes me wonder if you are just like them. So unless you want to convince me otherwise...
Leave if incall.
Tell them I'll give them something at the door to cover their time & expense.
And
Btw, if you don't like that, it's proof I owe you nothing.
Optionally, you owe me for wasting my time.