Can my website show prices in my customer's own currency, or does everything have to be in one currency?

Yes, a white label portal can normally show prices in more than one currency, so a customer in another country sees a figure they understand instead of doing the sums themselves.

The way it usually works is that the airline or hotel supplier sends the price in its own currency, and your portal converts it into the currency the visitor has chosen using an exchange rate. That rate can come from a live feed or it can be one you set and update yourself, and most systems let you add a small cushion on top so a movement in the market does not eat into your margin. You can also decide which currencies to offer rather than showing every one, which keeps the site simple for the customers you actually sell to.

What you need to be honest with yourself about is that showing a currency and getting paid in it are two different things. The currencies you can actually charge in depend on your payment gateway and on the account you hold with it, and some suppliers will only settle with you in their own currency no matter what the customer saw. The ticket or the hotel voucher may still be issued in the supplier currency, and the customer's own bank may apply its own conversion on the statement. Refunds normally go back in the currency the card was charged in, so the amount returned can differ slightly from what was paid.

Before you switch this on, check with your payment provider which currencies it can collect and settle for you, and decide where your exchange rate will come from and how often it should refresh.