I have a buyer in Russia who is buying my inherited property. I understand that I need to pay 30% tax as a foreigner on the selling price. Do you know how/to whome/when I need to pay this tax? Do I get he cash for transaction first, wire it to the US and then pay the tax?

What is also not clear to me why I need to pay tax at all when I sell this property on the full selling price -- as this is an inherited property - and there is no tax on inheritance in Russia.

... I understand that I need to pay 30% tax as a foreigner on the selling price. ..
Understand from whom?

Contact the State Department and get them to refer you to a reliable Russian lawyer who can guide you through this.