They way I was taught to approach a business owner/storefront was to first find the GM or owner, whoever is the one who is going to authorize the payment. (Quick Aside: I was asked by the employees at a local national chain pool store to clean the windows for $20 cash so they wouldn’t have to, but the corporate managers will not authorize external companies to do that work. They want the employees whom they are already paying to do it, but these people have no training nor proper equipment to do it the way we can. The regional GM found out and will not let the employees pay out of their pocket for me to come by anymore.)
Anyway, find out who is going to eventually pay and ask them: “Who cleans your windows? Are you happy with their work? How often do they come by?” When you get the answer to these questions, you can then adjust your answers and regardless of their answers to those questions, you are just leading them to think about the service they are currently receiving and then you convey that you can do better. (Your price may be higher, especially if they are having untrained employees using “Glass Cleaner” and paper towels, mean while leaving streaks and smears behind.) Say “I can clean these windows for you every Monday morning so that your products are always seen in the best natural light everyday. I’ll do the exterior for $1 per pane and the doors inside and out at each visit.” (You can adjust the interval based on their interest in the price and I would also adjust your price based on your region and how dirty the windows get during that interval.)
Establish a minimum price for your time. If it is a small storefront in a strip mall with a door, overhead square (above the door) and 2 top and bottom sections for a total of 6 exterior panes and the inside of the door, instead of charging $7, have a minimum of $10 or $15.
Be consistent. Be consistent. Be consistent. Develop your route and be consistent. When you are reliable, your reputation will grow and your clients will recommend you to others. It will be harder for another “Bucket Bob” to come in and low ball your client and under cut you if you consistently do a great job and keep your client happy. They will pay a little more for you to do the work consistently.
Always focus on the doors with hand prints and smudges by the handles and use a damp rag to collect any drips from the glass cleaning process left behind on the handles/push bars. This is a twofold benefit, the patron of your storefront customer is not going to want to touch a wet door handle, just think about if you were to grab something and it was unexpectedly wet, you would think “Did someone snot on their hand and then grab the handle? Is this ebola germs on my hand now? Ewww!” or whatever. But you are also making sure that there are no insects or arachnids (spiders) building anything in the handle pockets that can harm someone grabbing into a blind space.
Hustle. If you want to make good money, you gotta hustle. Hopefully you are either young or in good enough physical shape to move at a good pace. In a strip mall setting, you should be able to do a complete pane of glass in 30 sec on average. Some of these competitive speed cleaners can do a roughly 4x4 pane in 3-5 seconds. This is not a real world scenario, but your speed and efficiency directly correlates to your income. In the strip mall if you have 50 panes to do, and you do it at 1 pane per minute, you’ve made $50 per hour (or 83¢/min) with 10 minutes given to set up and pack up. But if you can do those same 50 panes in 30 minutes, with the same 10 minute set up/pack up for a total of 40 minutes, you have changed your hourly rate by 30% to $1.25/min (or $75/hr).