Wheres your morals? I don't touch other window cleaners custies and I expect the same in return!!
This is business. To operate within a moral framwork you should not deliberately target another window cleaners customers, but if you get a request for a quote, then there is no moral reason why you shouldn't give one.
The current w/c may be unsuitable for any of a number of reasons, all of which are the customers business, not yours.
I never ask if a prospective customer has a window cleaner already, and I certainly wouldn't ask how much he charges.
I give my quote, based on my charging structure and tell the prospective custy exactly what we do for the money. If they are happy with the quote then I accept them as customers.
Should they then tell me they already have a window cleaner I ask them to be sure to let him know his services are no longer required, as I wouldn't want any unpleasantness should my man and he meet up on the doorstep!!