Perhaps add seeding to your services. I agree, power rake and slit seed. Or...aerate and add seed with starter fertilizer. Be sure to offer the customer to improve their lawn permanently with higher quality seed. Disease resistant. Insect resistant. Drought tolerant. Darker green. Be ready to do a complete renovation; you will probably get asked that before long. Be ready to remove old and lay sod, if requested.
Change Bermuda to fescue. Or fescue to Bermuda. Zoysia?
And if you have Bermuda--add overseeding or lawn paint, for winter green.
And be sure to offer lime applications and soil tests.
Lots of people want someone to keep the weeds out of their shrub and flower beds. Lots of people want some kind of bare ground or cracks in the cement treatments.
Lots of people (in addition to fire ants and grubs) want perimeter sprays to keep insects and spiders away (fleas and ticks also) from the house. Easy backpack sprayer job.
Also get licensed for mosquitoes--can be big some years.