Ask what “free preparation” actually includes

This is an English reading overview of the Chinese article, rather than a complete translation. The Chinese source has been updated since this overview was prepared; consult the original for the latest details.

The central idea

The article raises concerns that some preparation services may involve machines or abrasive processes rather than patient cleaning, potentially obscuring marks or colour differences. Do not assume all services are identical. Ask how the pair was processed, inspect the condition and request disclosure of observed issues.