How long it takes
Check every broker. It takes one search.
Log in, search by MC number, DOT number, or company name, and read the status, the score, and the payment history. You are done before you have finished reading the rate confirmation, which is the reason to run it on every load rather than only the ones that already feel wrong.
Some do deserve a longer look: a broker you have never hauled for, authority granted in the last six months, a rate well above market for the lane, a phone number or address that changed recently, or pressure to accept without a signed rate confirmation. Those are reasons to read the report closely, not reasons to skip it on everything else.
If the load is going the other direction and you are the one handing it off, the same habit applies to carrier vetting.