Russian oil is trading at a ~$32 discount on the global market. China and India are the primary non-European buyers.
With the price of oil falling by ~10% and Russian oil exports declining by ~10% in recent weeks, Russia will have less money to carry out the invasion of Ukraine.
Russian oil is somewhat sketchy, and for the same reason, you can imagine the difficulty of getting the street price on an illicit drug. However the ministry of finance regularly reports the price it gets and contracts are traded on SPIMEX.
I think the biggest blindspot would be if any parallel deals are being made on other goods. That'd be harder to assess. But again that China is reducing imports suggests they aren't comfortable with paying higher prices.
Russia oil has a very low technical price point for oil producers of ~$40. But the fiscal breakeven is in the ~$70 range now, especially if the ruble exchange rate stays high.