Yes, many countries don't have the capacity to refine a large amount, but there are many simple techniques such as even heating the oil that any country can do.
There are always buyers up the chain and in neighboring countries that will buy it. Even arrangements from buyers across the world.
People ignore sanctions all the time. It's part of a free world and free trade. Similar to the legacy laws on the books that everyone and their mother ignores. It is much easier to simply go on with your life and when everyone ignores the law, it gets removed. Politicians don't want to be seen as weaker than they already are so they remove the law very quickly.