Am I missing something? Of course you'll be competing with these suppliers, you are all selling the same products! That's a pretty ridiculous thing to say.
It was a pretty good time about 5 years ago, not now.
Have you done any actual market research to see if what you plan to do is viable? What trades are you comparing to window cleaning? Builders, plumbers, electricians? They need supplies to do a job. They could and do spend thousands on supplies every month, the beauty of widow cleaning is you don't need that much (after the initial outlay) to run your company. How much does the average window cleaner spend? How much do you spend a year on supplies?
Not trying to put you down, its commendable you are looking or for a business education, but these are the fundamentals.