All cards have been cut by a blade. Different blades produce different cuts. Variations in the sharpness of each blade produce variations in edge textures even within the same sets. If a 1954 Topps card was cut with one of the rotary cutters with a dull blade, then it produced cards with a rough cut. These were only used on the left and right edges of the cards though, as a different blade was used to cut them horizontally (ream cutters).
Here is a link below to an article on CU regarding the manufacturing process at Topps with several pictures of the process. Note there are also videos and other resources available online of the operations inside Panini and other card manufacturers.
https://forums.collectors.com/discus...opps-cut-cards
If you believe that you can spot the majority of trimmed cards with a loupe, you're wrong. Especially with modern cards. You can learn how to detect a botched edge or a bad trim job, but you absolutely cannot detect a good one and neither can the most experienced graders at every TPG. And if you think AI is going to help with that, you'd be wrong again.
That said, you can certainly tell when certain cards have been trimmed. I encounter them regularly. But those were all trimmed by amateurs. It's like hair transplants. You can't detect a good one, only the bad ones. There are a lot of people walking around with hair transplants and you just don't know it. I wonder what there's more of, trimmed cards or people with hair transplants? I'd bet it close. Both are certainly in the millions.
As far as how to approach the market as a buyer, I think what the OP is getting at is that there is often no way of truly knowing whether or not a card has been trimmed. If it bothers you enough then you should probably study the subject, perhaps even cut up some cards yourself with various blades and examine them with a loupe so that you know what you're looking at. Then approach each card you encounter as having a likelihood of being trimmed or not rather than a "yes" or "no" determination. Cards with rounded corners are usually safe, cards with sharp corners that don't measure correctly are often not. If it's a PSA 9 or 10 vintage card and the borders look small, then it was almost certainly trimmed (and there are A LOT of these cards out there). Maybe take the Leon approach and only look for cards with large borders (although even large cards are not always safe). You can easily slice off 1/128" from a card. So if a card measures even just 1/32" tall, that means someone could trim it 4 times and still be within spec. And if you think rough cuts are safe, think again. This example below from a BODA post should tell you nearly everything you need to know about the trimming scandal. Note it measures the same size in both images.
As for me personally, I generally don't want trimmed cards unless it's a high-end card that I wouldn't otherwise be able to buy. Or rather I should say I don't want cards that bear evidence of trimming. I'm sure there are cards in my collection that were trimmed undetectably (we all have them), but as long as they measure correctly and the edges look like factory cuts, then I probably wouldn't care if I were to find out that it was trimmed. But I definitely try to avoid trimmed cards to the extent that it's possible.