Let's see now. The bow is a Mathews and it's 6 months old. You either have Zebra or Barracuda strings. You want to know if they have maybe crept a bit? It's all but a certainty. That's what they do the most consistently.

As for the shop guy? Do they sell Mathews? Did you buy the bow there? Of so, were it me, at the very least I would have taken a look at the cam's timing marks and if needed put the cam rotation back in time. We call that customer service.