Currently still, most companies want to receive in fiat currency. Most of these merchant payment companies function as a man-in-the-middle, so that you don't have to be concerned about anything Bitcoin-related.
They provide functionality with which your customers can purchase goods using Bitcoin and you will receive all payments in your fiat currency of choice (as long as it's supported by the merchant service).
Like with PayPal, when a users wants to pay with Bitcoin in your site, they will get forwarded to a page from, f.e., BitPay. The user will pay in Bitcoins to BitPay and be forwarded back to your site while you will be notified that the users did indeed pay. Meanwhile, BitPay adds the payment amount to your merchant account, in fiat currency, using the exchange rate of that moment.
Given the high volatility of the Bitcoin exchange rate, this is the best solution for most merchants for now. It's easy and safe.
So the companies basically carry the risk of volatility during the payment. Do we know how they handle it? In a bullish market this does not mind since you get more in the end, but bearish one is worse probably... – Kozuch – 2013-12-11T23:28:29.443
I guess most of them just sell the coins immediately at some exchange. I think I once read that BitPay keeps a large chunk of the Bitcoins they receive. If they did so the last few months, they were all millionaires by now. (Which I think they are anyway.) – Steven Roose – 2013-12-11T23:35:00.417
Yes but are they able to sell coins fast? They'd have to run their own exchange to be able to do this. Maybe they have an agreement with one of the big exchanges so they do not need many confirmations when transfering funds there for selling. Of course they could use an exchange as a wallet directly too. – Kozuch – 2013-12-11T23:42:31.400
1I think they might have special agreements with exchanges indeed. Otherwise it would be unfeasible. They will probably also always have a bitcoin balance at the exchange, trading instantly while the new coins are being transferred into the exchange. – Steven Roose – 2013-12-11T23:47:01.400
Also, they are free to charge their clients just the trading fee they can get at their exchange partners. – Steven Roose – 2013-12-11T23:47:30.713