How I check a design-to-code build before handing it over: I don't eyeball it.
I lay the design frame over the live page with a difference blend. Wherever they match, it goes black. Anything that drifted shows up bright, whether that's a 2px padding, the wrong font weight or a line that wrapped differently.
It takes five minutes, it catches what "looks the same" misses, and the client gets a screenshot showing it matches.