This is exactly where the market can step in and guarantee prices. As an example, I sell items directly for Monero, priced in Monero, and I use the 365-day moving average to do so. As I sell her, my service is taking on the volatility. And for that risk, I use the 365 day moving average, which means that in fiat terms, sometimes my items are more expensive, and sometimes they are cheaper. Either way though, in Monero, my prices do not change rapidly.