With respect to gear options, I've felt this way numerous times. When I got my first full frame DSLR, an original Canon EOS 5D. Then I had two of them.
Then, after upgrading to a 5D Mark II, then selling it and going to a pair of crop sensor 7D bodies, it happened again when I got my first 5D Mark III. It happened once more when I got a second 5D Mark III and sold lower level crop sensor bodies.
The 5D Mark III is a great camera for most everything. Especially if you have a lot of expensive long, fast lenses. I don't have a lot of long, fast lenses.
So, the 5D Mark III is not something to drool over when thinking about field sports or wildlife (without long, fast, expensive lenses). I spent the past week or so trying to figure out how to most efficiently improve my ability to shoot sports and wildlife.
A Sigma 150-600mm lens was considered. It's really large and not at all fast. The Canon 100-400mm lens, with the option of an extender, was considered. A bit too expensive, even used. Plus, that would mean using one of my 5D Mark III bodies, with it's six frames a second shooting.
I considered Rebel level crop sensor bodies for the 1.6x lens field of view lengthening factor but even though those bodies are inexpensive new, they all have some fatal flaw which ruled them out. So, finally, I decided that what I needed was a 7D Mark II to go with my 5D Mark III bodies.
These two cameras are remarkably similar in design and control layout. They differ mostly in the fact that the 5D Mark III is a 22 megapixel full frame camera and the 7D Mark II is a 20 megapixel crop sensor camera. But, the 7D Mark II is super weather sealed, has amazing autofocus and shoots at 10 frames per second.
Because the 7D Mark II is now about 5 years old, used copies of the camera are now a less expensive alternative than any of the alternatives I had been contemplating. So, once I made my decision, I checked out eBay and found a seemingly good looking 7D Mark II being sold by a camera store in Indianapolis.
The pictures didn't show much but the description said "heavy LCD scratches." Scratches on the LCD will not effect image making in any way and it's not a really big fix since what is scratched is a covering over the LCD not the electronic device itself. Plus, they have a 30 day return policy.
I should have the camera on Monday. Here is a shot of the LCD from the eBay listing which, as you can see, doesn't really show much.
You can check out side by side comparisons of the 5D Mark III and 7D Mark II here and here.
UPDATE 2/25/19: The camera arrived today and is in fantastic condition. There are no scratches anywhere that I can see. The body is in better shape than either of my two 5D Mark III bodies. And, the shutter count is less than 25,000 out of a rated 200,000.