Something ive always had a problem with is people will never water when you seed. Maybe one out of 20 will water at all. Ive tried slit seeding with mediocre succes and aeration overseeding and on those lawns that dont water only place i usually see germination is the aeration holes. its funny looking at first because the new grass is exactly the pattern of my aerator. I aerate maybe 2 inches for overseeding perposes. Really deep holes seem to close up and kill the new grass or no germination from being too deep i guess? Seems like the shallow holes hold water better than the surrounding ground which helps.
I think this fall im gonna sell slit seeding and aeration separately but do it on the same visit (shouldnt be hard to sell because in my experience the person who will pay for overseeding cares enough about their turf to pay for aeration.) basically I would aerate first then slit seed which would give me the best of both worlds and i could charge more money since its 2 seperate services. Just a thought.