Volvo v70 emmissions


My 2000 volvo V70 recently failed Massachusetts emmissions. According to the onboard computer, which is what they use to decide if a car is polluting, The fault was a catalytic converter. My service man nicely replaced the catalytic converter for a mere $1000, and a few days later, the car would still not pass the OBD emmissions test. Catalytic converter code again. I then visited a Volvo dealership to try to get a more expert diagnosis, and they think that since it was an aftermarket catalytic converter, it is probably burning at the wrong temperature for the OBD to accept. Now for a mere $1300 I could get an official Volvo cat that will solve this problem. Has anyone had any experience with aftermarket converters good or bad? Why has the state decidded to trust OBD more than a tail pipe sniffer?