emission test result bs??

I went to a shop to get a new catalytic converter..

they installed it but found that it wasn't working... they phoned me and left a message wondering what they wanted me to do next.. I never got the message, instead I just showed up near the end of the day figuring everything was OK. I think this pissed them off. Anyways he said he had a second cat in stock, and that he could weld it in while i waited... I heard no grinding or welding while i waited for an hour. A mechanic came out and gave me these results from his gas bench:

HC 67 PPM
CO .02%
NOX 3 PPM

the CO and NOX look suspicious.

I went to a Drive Clean centre next week, they gave me these results:

HC 146 PPM
CO .55%
NO 58 PPM

which failed me on the HC and CO. I went back to the shop, and got them to test it on their gas bench again... He revved my engine very high for atleast 5 minutes.. then came out and said "cat failed".

I figure they are messing with me. But I just wanted to know what you guys thought of their gas bench results before I try to get a refund. (I paid them because they said everying was OK).

Well, if he put a second cat in...as in he replaced the first, then its a bolt in affair. If he ADDED one then Id be suspicious. Also if you fail once, you dont just keep adding cats till you pass.

Sounds iffy to me. That's a pretty big difference between test's where there shouldn't be that much variation.