There have been unscrupulous sellers who will take an out of spec scrap part and put a serviceable tag on it and sell it.
Believe me, I know that to be the case. That is SOP in China.
The Chinese regulations require entire aircraft to be put out of service after a specified number of years. Those aircraft are put in mothballs but the parts are looted and just as you said, testing and inspection tags are attached to them.
Aviation parts are a big business. Parts are priced at a premium precisely because of the QA/QC pedigree requirements. The profits make it very tempting for criminals to try and sell used parts as new.
The FAA regulations for parts pedigrees are extremely strict in the USA and set the standards for the world. Without such strict FAA oversight, air travel would be much riskier.
I am part of an aviation parts association. From time to time I get notices and emails from the association. They are talking about using Block Chain Technology for tracking the entire life of FAA listed critical aviation parts. I think it’s a great idea. It could lower the price of parts and increase the security of the traceback.