Hey Justin, always check the siding for oxidation. Rub a finger on all four sides of a home and see if any chalk rubs off. When you perform this test, do it in an inconspicuous area so you don't leave a mark smack dab in the middle where it's so obvious.
Yes, you're correct, no one is going to hire you after seeing those results! With vinyl, there are solutions which can be used to help cut through the oxidation. I use "Reliable 1' which is an alkaline cleaner. Depending on the severity of the oxidation, sometimes I can simply apply a 75/25 water to Reliable 1 mix and using medium pressure, rinse it off. Other times, may need to go with a 50/50 mix and gently brush with a soft bristle brush and rinse. If you don't already have one, purchase a high quality "soft flock, full block" brush which you can attach to a threaded pole. Don't skimp on a quality brush.
With the proper house wash mix, you shouldn't need high pressure. Keep the nozzle further away from the substrate. If you do this to aluminum siding, you will most likely have to finish the entire side with up close and personal pressure washing. Never use an alkaline solution on aluminum siding unless you have a lot of experience!!! You could end up stripping the paint off!!!
Always make note of oxidation when giving an estimate and explain the situation to the customer...
Mike