The D600 was also recalled for an oil on the sensor problems, and several models were supposed to have been recalled to have batteries replaced in the box before (or at the time of) sale. I would not buy a recalled model without evidence that the camera had been sent for correction.

The OP made no request of what camera was the best for any use. In fact there was no request for counsel of any kind. Not around frame rate or card type used or anything else. The question was "what old Nikon was available for the best deal?" I interpret that as for a good, serviceable, reliable camera with good performance capability for a good price relative to its performance and original purchase price as well as against the price of a similar replacement. I provided my answer on that basis, and I stand by it.

Sorry if my response seemed to imply that the Z9 was the "best deal". That wasn't my intention. I was just pointing out that the "best deal" doesn't necessarily mean that the best deal will be able to do what someone wants their camera to do (besides the Z9 is not a DSLR, which was what the OP wanted). If the OP goal is to get a camera that will just take pictures of static subjects, I pointed out that the D7200 and D7500 are great cameras and can do much of what a D500 does and in some ways, are better than a D500 (use cheaper memory, have built in flash, etc).
And they can be used for action shots as well, just won't function as well as a camera that can shoot at higher fps.

The OP made no request of what camera was the best for any use. In fact there was no request for counsel of any kind. Not around frame rate or card type used or anything else. The question was "what old Nikon was available for the best deal?" I interpret that as for a good, serviceable, reliable camera with good performance capability for a good price relative to its performance and original purchase price as well as against the price of a similar replacement. I provided my answer on that basis, and I stand by it.

I disagree with Paul a little bit here. I'd be a little bit iffy about buying any of the top DSLRs used unless I knew and was very confident of how they had been treated. They are very complicated gadgets and it's pretty easy to damage their internals. Just be very careful.

There is no question that the D850 is a great camera. But 46 MP is a lot and can sometimes be a burden. If you can't really justify it, I'd look for a D810 instead. It's available for a lot less money, has an incredible smooth, quiet shutter, and will do probably 98% of what a D850 can do, just at 36 MP, which is plenty most of the time. There are some really nice D850 features missing from the D810, but nothing that will prevent you from taking great pictures.

For a DX camera, there's really nothing else that comes close to the D500. They are not quite as easy to find, and the ones I've seen in what I
consider buyable condition can be more expensive than the D810.

I've not looked at consumer grade cameras on the used market, so won't speak to them. I do own and shoot all three of the cameras I've discussed.

How about just a self-proclaimed camera market expert? Personally, I think a used D750 is the best mix of recent technology and price. You can pay more for the D780. But really, for what? It's just another (final) 24MP full-frame DSLR.

The D850 is the final and best release. But never and I mean NEVER spend new money for an old DSLR at a new camera price. Buy a used one and figure it's the last camera you need this life-time, same as the D750 should be.

You can go further back in time, but why? They'll never make another new DSLR, so go with the final (ish) versions.