[xnx]

> The only really good test is to use the product for many years

Agree. However, a good reviewer should be able to transfer knowledge from many years of use about a similar product to a new product and give an insightful evaluation. This type of reviewer is exceedingly rare.

[kevincox]

I think a very knowledgeable reviewer can make a decent guess. But to really know you would need to tear it apart and analyze all of the materials used (maybe the metal or plastic has been swapped to a slightly different material which is very hard to identify by just looking or touching). You need a team of engineers. Probably the best you can hope for is noticing a part is changed and make an educated guess why it was changed.