When I had an issue, they replaced mine, no questions asked. I bought a second one and have not had any issues with it, well over 5 years. I have an A100 that is almost 10 years old now, no issues. So I don't think there are any real issues with their amps and I never had any problems with service.
The second prepro I had from them had frequent issues however. They replaced it for the price of shipping one time, but the second time I would have had to pay for service and I probably wouldn't buy another from them.