I thought the idea was that we know that sanctions are circumvented this way, but it puts a tax on all dealings.

Russia selling oil to India? It's now part of the world oil market, so decreases demand from India for other nations oil. Effectively they're still selling the same amount of oil, but now they get rupees instead of $, € or ₽.

Russia selling wood through Kazakhstan? Well it's the same wood being sold, but Kazakhstan is getting money out of this somehow. There are people to bribe on the way. There are logistics to be done. They will achieve a lower price on the wood now.