Usually it is best to begin by defining a few terms. In any sales business, there are at least two different values for a single item. A wholesale value is the price of an item when it is purchased from a supplier by a retailer. A retail value is the price of that same item when it is sold to an end consumer. This final price is the retail value.
Stamp catalogs list the retail value of a stamp at the time when the catalog is published.
In other words, the catalog value of a stamp is the price you should expect to pay for that stamp if you were to purchase it from a dealer at full retail value. Within the stamp trade, there is a thriving wholesale business. Dealers regularly purchase from other dealers stamps that are needed to fill orders. The prices paid for stamps between dealers varies widely based on the relationship of the dealers, the stamp itself, a the current market conditions. It is these wholesale trades that really set the pace for the stamp market.