The customer is not king when they speak to you like a servant.
They need your services, you supply it. When they are rude, arrogant etc then dump them.
If a round is so fragile that you are dependant on every penny and every account, it is time to reconsider your round and look at pruning it.
Any business advisor or mentor will tell you that in order to succee, you need to concentrate 80% of your efforts on the top 20% of your customer base and attempt to replicate this 20% through the rest of your business.
Look at it like a Christmas tree with the top branches being the healthiest and bearing the most fruit (the 20%) Look after these branches with care and the healthy branches will start growing richer and bearing more fruit. As the top of the tree starts becoming more bountiful, prune off the lower unhealthy branches (the late payers, the rude, the bad access, the not this time please etc etc)
Eventually, you will have a fantastically bountiful and healthy tree (business)
The good customers you now have will spread the word amongst their circle (more of the same) the dumped customers will continue telling each new window cleaner that the last one was so unreliable !
Be the boss of your business

Dump the dross.