The way the ability to buy with cryptocurrencies is usually implemented like this,
1) The site owner puts an automatic fiat-crypto conversion in the background
2) They put a price in fiat on each item, but the users only see the crypto-price
3) When the user decides to buy something, the conversion price will be locked for X minutes and the system will await the payment
But I guess you mean that a company (in this case the XDNA team) is in risk of buying an item for 9$, selling it for 100 XDNA (10$) and later the coin's price fall 20% and it's like they sold it for a loss of 1$.
I don't think it makes much of a difference for XDNA because if this operation would be a success with many sales, then the coin's price would rise striking a good profit. If the shop would have only a few sales and the price fell, then this wouldn't make much of a damage because of low sales.
for example this update: " 2018, Q4
Release a mobile wallet for Android"
CryptTech, I have not ignored your question, I'm just waiting for someone from the dev team to answer me. They're on different timezones or sometimes they're just busy! I'll follow up with you soon though.