It's part of the business we're in.
Call it an occupational hazard!
I always ask a customer 'would you like it cleaned just the once?'
I never mention a regular clean.
That single question usually sorts them out.
If I think the customer is genuine (and don't get me wrong, 50% get dumped over the phone) then I will charge a first clean price and then a regular 8 weekly price. If the custy is happy then I go ahead.
These days I get it right about 90% of the time. Occasionally I get it wrong...but only occasionally!