[petsfed]

>This stuff is hard to get right and there are endless gotchas and exceptions and edge cases and you have to know about and account for all of them.

And this is also a major source of the cost of the testing. You're not just paying $5k+ for a piece of paper that says "FAIL" on it, and "better luck next time". The test engineers want you to pass, ultimately (if for no other reason than because you can't get repeat business from a customer who goes out of business), so they're going to point out the common sources of harmful EMI they've seen in other designs.