Id say for discounts is the only reason why they would choose to do so.
In order to make a payment to someone, there are a lot of middlemen who earn interest. In the case of bitcoin is not the case. But in bitcoin can make a waiver or change the terms of payment. This is also an important aspect.
So the customer who pay with the bitcoin should pay lower price.
Rather, it will depend only on so much appreciated at the moment bitcoin and what value it will have at the time of purchase. If we take into account that someone will be interested in product sales for bitcoin, it will only add more for a number of special customers.