This is an excellent question with no simple answer. Here in Canada, for non-Canadian coins prices are usually quoted in US dollars so in principle, dealers need to adjust to currency fluctuations. In practice they can't change the prices every few weeks, and usually give a discount off the catalogue, so they could adjust the discount if there are significant changes, or not if it is a small value item that they've had for a while.
In general it can be difficult to keep track of all the market prices and fluctuating currency values, so there is some risk of setting the wrong price. For large value items they would use current auction/ ebay prices and current exchange rates.
In general it can be difficult to keep track of all the market prices and fluctuating currency values, so there is some risk of setting the wrong price. For large value items they would use current auction/ ebay prices and current exchange rates.