What you can say Gabi is "I'm very sorry but I do need a minimum of 1 hour's notice so if you would like to make an appointment for 1 hour from now that would be great?? Or maybe for some other day when you have more time?? Thanks for the interest" .............. you don't tell a potential business client to "fuck off" because he is anxious to see you!! No excuse for rudeness on the phone from either side in this game.
Paws