LOL, no there are not tractor emission inspectors at the Ag entry stations. BUT, I work for a nut harvesting equipment manufacturer. And any time we have to change an engine, we have to punch holes into the old engine block, take pics of the holes in the block, and send those to the engine supplier. Because the emissions controls are so strict here in California, CARB does not want a possibly used engine being rebuilt and put into service. Which, by their reasoning, there would now be two engines adding to the carbon footprint. The new one going into the old machine and the old one which was rebuilt going into something that did not have an engine. There is no such things as buying a new engine for a machine and having the old engine remanded for a spare here in California. IF you buy a new engine, the old one MUST be destroyed. I know, I know it doesn't make any sense. But that's how things are here.
Plus, the price of new Tier 4 machines, farmers and tractor operators are using the machines longer to ring out as much cost savings as possible. So there are very few newer used tractors available here. If you do find an used tractor, it is either a one or two year old rental return or it is a very old tractor.
But, it's not like I am doing net searches every day. So I could be missing some good deals in between. When I do search though, the good deals are almost always east of the Rockies. Or so it seems. Oh well. B.