natural prices can only exist in an environment where every consumer and producer has all the information and is completely rational.
if you are rich and a vegetable seller who typically charges $5 for a vegetable charges you $10 you are unlikely to bargain as you would consider it a waste of your time and energy and just buy it. is this person being rational by not wanting to waste their time or irrational because they aren't squeezing more out of the seller.