I finally checked my credit report, here's what I found
Three years of putting it off, and the whole thing took eleven minutes.
I'd been meaning to pull my credit report for years and kept putting it off, half-assuming it would cost money or turn into a whole afternoon. It's free from all three bureaus at annualcreditreport.com, and it took eleven minutes including the part where I dug up an old address to verify my identity.
What I actually found: an old collections account I didn't recognize at first, which turned out to be a medical bill I'd paid off months earlier that the provider had reported slowly and inconsistently. A credit limit on one card that was a couple thousand dollars lower than what I remembered. No fraud, thankfully, but I know people who've found accounts they never opened.
The specific things worth scanning for: accounts you don't recognize at all, late payments on accounts you're sure you paid on time, balances that don't match what you actually owe, and closed or paid-off accounts still showing as open.
Disputing something wrong is a form on the bureau's website, not a phone fight. I filed a dispute on the collections account with a note explaining it was paid, attached the payment confirmation, and it was corrected within about three weeks.
Checking once a year (staggering which bureau you pull, since they don't always show identical information) is enough. It's a boring five minutes almost every time, right up until the year it isn't, and that's exactly the year you want to have already been checking.