After a spate of 'Not this month, mate' last year I got a 'cob on', and printed on my chits my terms and conditions of service, which basically says I come once per month, unless they have arranged other terms and conditions.
It's rare I get someone who says 'Not this month, mate', now, and if I do they're normally new customers who haven't had our chit.
If anyone ever says the equivallent of 'not this month'; we drop them. I sometimes discuss this with the potential ex-customer, but usually, I just drop them.
I think it's really cheeky, when you've previously agreed your terms and conditions and then the customer attempts to change them in their favour.