Re: Possible Ways Duplicate Leads/Contacts Can Be Created
I'm going to rattle off a few, and hopefully other people can chime in as well as I'm sure I don't have them all in my head.
Creating a duplicate manually/through API in Salesforce and it syncs over. Doesn't dedupe through Marketo, so retains the dupe.
Manually creating a lead in Marketo with duplicate email address.
When two leads are created at the same time through two of the following options: Salesforce, Marketo form, API into Marketo. If leads are in the creation process at the same time from two sources, they won't exist in the database to deduplicate against yet.
This can be as long as a 7-minute process, especially when leads are getting synced over from Salesforce.
I've also run into problems with having a Marketo form fill-out followed rapidly by an API sync into Marketo creating duplicates. If you have a third-party integration with your product database pushing new users into Marketo as they're created, this comes up moderately frequently.