New cat is mad money and second hand ones are rarely parted with as lads need em for NCT's... also they never last long if they've been off a car for a while. I bought one years ago and it blew a hole after a few weeks as it was sitting in a storage for a while and moisture rotted it from the inside out. Straight in the bin! Basically you never know what your getting buying secondhand... or if the cat even works efficiently!