ok... project yourself... its the month after christmas and your gas bill has gone up by 40 quid per month 
are you going to get rid of the window cleaner who charges £10-£15 per month???
I dont think it will be that cut and dry.
Yes, I do think we're heading for some pretty grim times in the next few years. But it wont be the end of civilisation as we know it.
Being "aware" that things are different from the last decade and will probably get worse before they get better is a good way of hedging your bets.
Example -
1. Customer lives in an affluent area, lives in a detached house and drives a Bentley.Will he be affected by the crunch? Yes. But everything is relative and cleaning his windows is a very very small expense to him compared to his income/expenditure.
2. Customer is retired. No mortgage. Drives a decent car.Affected by the crunch? Yes, his savings are not rising as fast as fuel/food but he has always had his windows cleaned and will probably 'weather the storm' without too much trouble - maybe he will go 8 weeks instead of 4 weeks.
3. Young couple, bought their first house recently. New estate. Drive quite nice cars which are probably new or only a year or two old and she may have just had a baby (reducing their income?)Affected by the crunch?
MOST DEFINITELY!! they have most likely borrowed well beyond 3.5x salary and have other large commitments such as credit card debt, car loans and the like. These customers will have no choice but to cancel or end up owing you money.
This isnt an exhaustive list of all the possible permutations, but it does highlight the need to put a little bit of thought into who your customers are, what brackets they fall in to and the possibilities of default from some sections.