The bottom line to keeping your business and personal credit strong is straightforward: Don’t borrow more than you can afford, and pay all your bills on time.

But what happens when your credit report includes a mistake — especially one that makes you look less creditworthy than you are?

Credit report mistakes do happen, although there’s some disagreement about how frequent they are. The big credit bureaus — TransUnion for consumers, Equifax and Experian for both...