First, let me say this is not the place for this challenge, I understand what you mean and what you are saying. The replies that are posted in this area are opinions and experience not hard fact.
SO, IMO the "rubber stamp" rule you are refering to is a rule of thumb because once something has been labeled "used" most people feel that half price is the going rate.
To quote a portion of my last post:
All parts that are used will get a 50% cut from the "new" price unless it is in very high demand and/or some one wants it bad enough.
This rule of thumb is true a lot thus is why it was said.
If you disagree that is fine you are entitled to your view but take a look around not just this forum but others. Also think about this like a car, once "used" the price drops off significantly even if its 3 months old! If you sell it to a dealer you could get one price. If you sell it to another person privately you could stand to make more on the deal. Everything can change and all transactions are different.