This method of obtaining aircraft by a country subject to sanctions isn’t unprecedented. In 1973 Air Rhodesia acquired 3 B720s and filed flight plans for various destinations in Southern Africa. At the last minute they simply diverted and flew onto Rhodesia.
Their Air Force was able to acquire aircraft and spare parts through diverse and ingenious methods, and remained highly effective throughout the war.
Sanctions make middle men rich, depending on the nature of the goods, price premiums from 10% upwards and discounts of 10% and more are needed. For something that can simply be relabelled to disguise its origin, such as beef, the discount is at the lower end. Spares for military aircraft are subject to much greater controls and premiums paid are at the higher end.
One thing is certain, the broker involved in the B737 deal made a lot of money.