Fortunately, I've spent time working on the car with my "shade tree" certified mechanic so I came here knowing exactly what my car needed: new cats (catalytic converters). My car had very little air coming outta the tail pipe. This indicated a clogged exhaust system.
My Hoopty (1993 Ford Explorer) has double cats, so my mechanic had pre-schooled me on just what to tell the Shop Manager as far as how he could possibly get by with one cat. The Manager agreed with his logic and, they chatted. My mechanic was offered a job there to which he politely declined. One cat would significantly lower my repair cost. In the end, however, the Manager opted to go with specs and gave me the second cat at a significantly lower cost than I would've paid originally. Mind you, this doesn't mean that my wishes were over-rode, for the higher dollar repair.
Overall, I was pleased with the service and repair. Would I return? Maybe. Like any repair shop, the Buyer must beware!