My guess is someone replied to that ad in SGN about getting an auto sear for cheap. Ya, the one that doesn't even tell you that you have to be representing some police agency and it has to be for said police agency.
Somone might think 'hey, why would they sell something that is illegal here?' if it doesnt even have the fineprint that its not for sale to common people.
Besides, how can anyone tell what you have in there unless they are a cop (that knows what to look for which most probably dont) and you had it to fire auto all the time unless you modified the selector switch and added an extra hole for the other needed parts. That would definately be a dead giveaway. Then they would come over and ask you for that so called "license" which you don't have since you think you don't have a machine gun to go with it anyways.