Sales says the leads marketing passes them are low quality. How would you investigate and respond?

I would resist both reflexes — defending the model, or lowering volume — and get to data first.

I would pull the last quarter's MQLs and segment them by grade and score, then join to what sales did with them. Usually one of three patterns appears. If low-grade prospects are getting through, the grading profile is too loose or the criteria no longer reflect who actually buys. If high-grade prospects are converting badly, the issue may be scoring — passive activity like email opens weighted too heavily, so people who are merely present look interested. If the leads are fine but sales is not working them promptly, it is a process problem, not a scoring one, and speed-to-first-contact will show it.

I would also check for pollution: job seekers from the careers page, competitors, and existing customers all inflate the funnel and are fixable with rules and suppression.

Then I would take a specific proposal to sales — adjusted thresholds, a named exclusion set, and an agreed disposition process — rather than a general promise to improve quality.