If you are looking at their website using a browser connected to the internet, you don't need to do currency conversions in you head and memorise the exchange rates every morning, you can just use that same browser to ask for a currency conversion from any of a number of sites, e.g.
If they are charging in CHF, then it's in both their and their customers' interests to quote in CHF, otherwise fluctuations in currency markets and variations in the exchange rates offered by their customers' banks will invalidate those quotes.
https://www.google.co.uk/webhp?#q=1%20chf%20in%20usd
https://duckduckgo.com/?q=1chf+in+usd&ia=currency
http://www.wolframalpha.com/input/?i=1+chf+in+usd
If they are charging in CHF, then it's in both their and their customers' interests to quote in CHF, otherwise fluctuations in currency markets and variations in the exchange rates offered by their customers' banks will invalidate those quotes.