I wouldn't go back and "try" to fix it for him. He will find something else then to blame you for. If he has paid. Leave it alone. The type of person he sounds like, he won't have many friends. If still getting a hard time from him find a roofing contractor and take him to look at the roof. He will be able to see right away that the shingles are from a different lot number. I see that a lot with certain roofers around here.
Some Roofing Contractors will blame YOU, to try and get a re roof job! Be careful !!!! You cashed the check, and did your job. Now, walk away nicely, and realize some people will never be happy, even on a Prozac Drip.
The only person I would consider taking a look at is would be an independent Home Inspector that had nothing to gain from it. Then again, they don't do it for free.
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Prime Choice Power Wash LLC Roof Cleaning Kissimmee Florida