Be sure to offer several kinds of organic products that your competition does not--even if you do not use such products on every lawn. Barry's Screamin' Green fertilizer for instance. Give Phasthound a call--he can help you.
Optional compost tea. Optional fungus mixtures that decompose thatch. Compost topdressing. Optional worm castings, seaweed extract, beneficial soil bacteria...
"Mineral-based soil sweeteners with magnesium".
Also offer disease-resistant grass seed (non-GMO) that doesn't need chemical fungicides.
And offer endophyte-enhanced grass seed that is resistant to insects.
Offer clover seed that produces its own nitrogen.
Organic insecticides should be available if the customer wants them.
And be sure to arrive in a hybrid, propane or natural gas powered (or flex fuel) vehicle, and use propane powered mowers and ride-on spreaders.