These guys messed up on my taxes 2 years ago, which led to me underplanning my tax liability last year by several thousand dollars. When I asked for some compensation (like a discount), I was told that "it's not that much money, so I shouldn't worry about it."
As a result, I had to pay my taxes late, pay interest and file a revised tax return from 2 years ago (and pay even more). They took no responsibility, even though the entire concept of their business is handing the intricacies of international tax law (they misapplied the totalization agreement for self-employment taxes, which is basically the definition of their job).
Stay far, far away.