While that may be true for other people, I have no trouble giving a purchased object a rating for its objective value (but I do excessive research on buying options beforehand). Even if the judgment is relative to other products, it can still be objective.

The rating may be inaccurate because you can only measure in full stars, but it'll still be objective and the inaccuracy is the fault of the rating system, not me.

Objective (adjective):

> (of a person or their judgment) not influenced by personal feelings or opinions in considering and representing facts.