The catch was my parents had to pay $180 to replace the exhaust piping as the standards had changed since the original house was built (1996). Well, I told them it should be their responsibility to make their tank work. After much haggling, they reduced the price to $125 but refused to waive it altogether. After 15 years of renting, the one time my parents call for service, they have to pay??
That's a gas code change. Your parents would have had to pay for the exhaust upgrade anyway, whether DE did it or they brought in their own contractor.
I had to upgrade my venting as well when my water heater died a couple of years ago. I agree the cost is a scam. There is $40 in parts at best and the job takes all of about 10 minutes.