If I delete leads from just Marketo and not SFDC, how does the backwards sync work? Do the existing leads in SFDC sync back to Marketo? Or does it stay deleted in Marketo? How does Marketo know that those shouldn't be synced back after being deleted? Thanks.
The next time the record is updated in Salesforce it will sync back down to Marketo and create a new record. You will need to find a way to stop records you deleted in Marketo from being visible to the sync user, either through visibility rules or asking Support to set up a sync filter.
Question on this as it just happened to us...
I deleted several thousand leads from Marketo, but not in SFDC, thinking that the lead would only sync back to Marketo if the record was updated in SFDC. However, the next day, they all sync'd back to Marketo, showing a bunch of old campaign activity in the log as being new. Wondering why the SFDC campaign history data would have triggered the lead to sync back to Marketo when it happened months ago?
Mostly driven by our cap limit on leads in the Marketo DB. I don't want to delete them out of SFDC also, because I don't know whether we will need them in the future.
We have a sync to Marketo field in SFDC so if we uncheck the box then the lead won't get back over to Marketo. So, when I delete a lead in Marketo I will first make sure that box gets unchecked, sync to SFDC and then delete the lead out of Marketo. It's best to work with your SFDC admin to be able to create this sort of thing so that you don't have to have every lead in SFDC in Marketo.
You also have to keep in mind if there are ANY updates on the record in SFDC it will be pushed back into Marketo. Not just when a sales rep works the lead, but any update to any field will trigger the sync.
There was a great post written about how to create a custom sync filter here: Instructions for Creating a Custom Sync Rule
We did a little testing to attempt to solve this issue and came up with the following: We created a new SFDC Custom Field for "Lead is Deleted in Marketo". We then ran a batch campaign for the leads we wanted to delete that changed their data value for Lead is Deleted in Marketo from false to true. That then syncs over and checks off the custom field in SFDC and the logic then unchecks the "Sync Filter" checkbox to prevent them from coming back into our system. We then are clear to delete the records from Marketo.