Took me a while to figure out what exactly is going on here, but it is ultimately ebay's fault. What they're doing is upscaling lower resolution photos, but using AI in the upscaling process. Their main photos are upscaled to 1600 pixels wide (hence, why the image name ends in 1600.jpg). But if you simply change the direct URL of any photo to 800 instead of 1600, then you get an 800-pixel wide photo but without the AI scaling applied, so long as the original was at least 800 pixels wide (but less than 1600).
What it ends up doing is trying to add detail that isn't really there, and it is terrible at doing it.
Here are the direct links to the 2 image files for that GS 7600 video card:
https://i.ebayimg.com/images/g/pOMAAOSwn~pnjYo3/s-l800.jpg
https://i.ebayimg.com/images/g/pOMAAOSwn~pnjYo3/s-l1600.jpg
Pay particular attention to the nvidia print and the print on that black chip. It looks more natural in the 800 image.
The sound card photo that I started this thread with is even worse as you can even see AI applied to the 800 pixel image - you have to pull up the 400-pixel image before it looks natural (albeit blury). So apparently the original was less than 800 pixels, thereby exaggerating the AI effect when upscaling it to 1600.
I guess the lesson here is, if selling on ebay, make sure your uplaoded photo is at least 1600 pixels wide or else incur the wrath of AI upscaling - something that it appears you cannot disable.