OK, another merchant version - if your credit card company reversed the charges, that means the merchant didn't respond to your inquiry (the most likely situation), or didn't respond in a meaningful way (meaning he/she didn't prove that you owed the amount). If what you are saying is true (and I must assume that it is) - then stick by your guns. #1 it is unlikely that the shop is going to come after you for the cost of the shocks, as the cost of litigation is much higher than the cost of the shocks, #2 if he does come after you, it sounds like you have an excellent chance of prevailing-given the facts in this matter.
The bad news is that ANYBODY can take you to court for ANY reason they want. The extra bad news is that common sense doesn't always prevail in a court of law. But given what you have told us here - which I must assume is the whole story - you should prevail. The bad news is that if the merchant is stupid enough to press charges (I say stupid enough because even if he wins, the legal fees will exceed the judgement), you will spend a consinderable amount of money defending this matter. My advice? Stand your ground, tell him the facts - let him talk to the other shop that made the final repairs, and tell him you do not intend to pay him for work that was not done completely/to your satisfaction.