I seriously doubt they are skimming. It's most likely the company that is actually doing the currency exchange that is overcharging AirBnB and they are pushing the cost onto the end user.

It's a fairly common practice for states in autocratic regimes to force foreign businesses operating in their country to cut them in on the action with currency hijinx. Currency exchange rates are often purposely kept low for precisely this reason. Even if it's the exchange company ripping them off, at least half is going into some bureaucrat's pocket.

It's a cheap way for the regime to reward supporters without actually having to come up with any real dough. Anyone supporting the regime has safe, easy means of exploiting currency arbitrage whereas ordinary people are policed heavily. Show up at the airport with a suitcase full of US dollars and depending on your political status the customs agent will either close it back up and send you on your way, or perp-walk you straight to jail after confiscating your haul. (guess where it's going?)

It's also why one of the first demands the IMF makes on broke states before they'll lend them money is to let the official currency rate float.

This does not apply to Russia, countless other sites allow payment in USD/EUR, so it looks like management decision

In that case then why don't they allow paying in either currency? I hate that airbnb always makes me pay in my home currency when my credit card gets me way better exchange rates, but I don't have a choice

no way they'd allow someone profit off their users like that without getting a huge cut for themselves