I spend years as the global quality manager of the fourth largest adhesive manager in the world. I can't tell you how often I received calls from salesmen wondering why my department had put on-hold a product which was only 10 centipoise lower in viscosity than the customer specification, and even more amazed when I told them that we either had to adjust the viscosity for that lot or get the customer's written authority to ship it, as required by ISO 9000, to which we were registered, and to the customer specifications, which we had signed and agreed to meet.
Of course you're right about the subjectiveness. But isn't it odd that sellers overevaluate and buyers seem to have a genetic predisposition to underevaluate.