Do this in fall if possible. When soil temp is above 75. Slit seeder is better. Aeration machine is not really designed to prepare a seed bed. I suggest seed first then double aerate to get most of the soil on top of the seed. I suggest sow double the usual amount of seed to be sure some it "takes". And don't use the cheap seed. Use a high-quality brown patch-resistant seed like Falcon 4, and add about 10 percent bluegrass to promote better self-repair. Expect slow germination due to low soil temperatures. If the customer wants to do it cheaper, let him sign off on use of less expensive ingredients. Naturally do not guarantee anything.
Naturally, you should be aware that crabgrass control would block the germination of any new seed. If you can find someone who is licensed, he could possibly apply crabgrass control after the new grass was up--after two mowings. Its a gamble because it would be rather late for crabgrass control
let us know what happens.