Failed seed jobs require some advance planning and precautions and some detective work. Always save a sample of the seed and the label. So you can show them the test date and the germ percentage and the weed seed content. Let them sue the seed testing lab. Always save a sample of seed so you plant about a hundred seeds in a coffee cup on your desk or window. That way you know the seed is good and you can show the customer. Read their water meter. Ask for a copy of their water bill.
The HEAT plan is excellent.
Take a careful look at the seed result. If it looks better in the shade--the sun dried out certain areas. Learn to recognize pythium seedling blight.
I did a couple seeding experiments about a month ago. I seeded right through crabgrass. We had some good rains. Today the new grass is coming up right through crabgrass. No soil preparation whatsoever--no irrigation whatsoever.