I was recently setting up a webinar campaign in Marketo and noticed registration numbers looked a little higher than expected. (In an ideal scenario, I should be happy about it, but contrary to it, I was skeptical!)

When I dug into the records, I found that some attendees already existed in the database. Instead of updating those records, a few were being created as new leads because the data from the webinar platform didn't consistently match.

What surprised me was how normal the situation was. Nothing was broken. The integration was working. The records just looked different enough to be treated as new people.

It reminded me that duplicate leads often come from everyday marketing activities rather than major system issues.

Lately, I've been thinking more about preventing duplicates before they enter Marketo instead of cleaning them up later.

Some teams handle this with validation rules, while others use Marketo deduplication tools to help standardize and match records earlier in the process.

Has anyone else run into something similar?

What's been the biggest source of duplicate leads in your Marketo instance, and what have you done to tackle this issue?