It could be argued that those two examples are good cases where the customer could be concerned about the value they get, even including the status factor. Diamonds are notoriously high-priced because of a quasi-monopoly, and high-end clothing is pretty often of poor value, quality-wise. If you like designer clothes--and you're not on unlimited budget--you eventually learn what designers/brands to avoid, because the value is just not there, even for that industry.
So this looks like a case in point, where having a rough ideas of the production cost (some parts hand-made, made in France/Italy/England, expansive material like quality cashmere etc.) is important.
only approximately, and only if the consumer really knows the cost.
Think jewlery (like diamonds), or expensive brand name goods like designer clothing. The production cost for those goods is "low", but the charge is in marketing and status symbol representation (which is modified via marketing).