Bitcoin price goes up and down all the time. If someone buys something costing 10$, the next day it may cost less or more. So it's a risk for the seller.
You mention the main risk about accepting coins, if the coin drops 30% then all your prices will drop that percent. And is a not cool loss at all.
Some people think it's possible if the value of the things is based in dollars and paid in bitcoins, but the only way to make this with low risk is by selling the btc at the moment you get the payment... But even if we do that and the price goes up after we sell then it will represent a loss.