Dealer service says I need a new Catalytic Converter front and rear plus misc parts..

[Ghost-Flame]

So I take the X in. to have them read the codes. 2002 3.0 165000 miles.
He says he is getting a catalytic converter code... Immediately he tells me I need new catalytic converters parts and labor over $3000.

Wait why would you jump right to that conclusion? he can't tell me if its the front or the rear, says it could be just a sensor... but his advice would be to replace the whole cat system. of course at that price... for him.

Anyway my indie says a lot of things could be wrong causing that code that are much cheaper and he could do a whole job for less than half the dealer cost.

Do you think I could find a good used Cat System from a junk yard with say under 60,000 miles on the system? And how can I test the cats to make sure they are good?