This old chestnut again :
There is no legal reason why you should not leaflet and canvass wherever you like, I do it all the time.
HOWEVER - in the interests of fair play and avoiding nasty confrontations, it is advisable not to POACH. That is, to deliberately target jobs you know are done by someone else, with the intention of undercutting or using some other dubious method (like telling his customers he's a part-time burglar, for instance
) in order to take work off him.
I have a self imposed strict code of conduct when I canvass - I knock on the door, introduce myself and offer a quote for my services. If the person says "I already have a window cleaner' I say 'thank you' and walk away. Sometimes they will say as I turn away: 'What would you charge anyway?'
I then give them my pitch, explaining the benefits of WFP and using an established well known firm, and give them a quote. I DO NOT ASK WHAT THEIR CURRENT WINDOW CLEANER IS CHARGING.
If they decide to change to me, that's their prerogative - they've made the decision and I can't be accused of poaching. my quote may be higher or lower than their current price, I don't know or care.
Providing I stick to this formula I know I have acted fairly and ethically. If the other window cleaner takes offence, that's up to him. If there's any hint of threat or intimidation I would report it to the police.
I'm happy to say I can't ever remember any occasion when this happened.