bugeye cel light

am going up scotland to have a look at a nice bugeye tommorrow. the car sounds great and engine wise is standard except a exhaust and decat.
the guy says he fitted the decat and the cel light didnt come on but took it for a mot and says the tester messed on with the lamda senser and soon as he got the car back the cel light comes on.
says it drives the same but just wondered is this common or should i be a bit cautious of this.
looks like its been well looked after

CEL comes on when people decat without 'fixing it' through a map, adaptor or similar

However cars are a lot of pennies and think I'd want confirmation the CEL code is for cat not working right which is P0420 IIRC

be careful, inspect the car out before you buy

had a bugeye here recently with the same problem, and after 2 hours ov messing around, i found the wire harness had been butchered big stlye, and cel light could/wouldnt clear, so be careful mate

(this was a dark blue bugeye) hope its not the same car

its this car

http://www.pistonheads.com/sales/1742148.htm

iam going up with my mate who is a mechanic but he isnt clued up on subarus.
suppose there is only so much i can check. aslong as it runs as it should with no misfires and stuff i will probs buy it and take it easy til i can get it checked out back here.
my mates got a standard 05 blobeye so iam expecting this to be just as quick.