when someone rings up firstly i listen to there voice, are they young? are they common? then I ask where they live, if they live outside my area (or in my area but on the council estate) I will then decide (using the above info) if they are worth quoting too. If they meet my 'preferred customer profile' then I will go out to give them a quote even if its just a bathroom.
so to make it simple if they are poor, common, young, or live to far away I blow them out. all others get an in-home quote.