We've all had these moments of dread...
Your Salesforce admin pings you on Instant Message, and asks you... "Why is Marketo (or Hubspot, or Pardot, etc.) updating {insert random data value not associated at all with Marketing}?" You go into your marketing automation system (I'll use the Marketo Engage use case here), and do some research about why the data change occurred.
You then find that the record was indeed updated, but in the Marketo Activity Log you can clearly see that the record update was made by "sfdc" (Salesforce).
After conducting this research/troubleshooting, reply back to your Salesforce admin and tell them that Marketo is telling you that the record was updated by Salesforce.
The Salesforce admin, however, reply back to you and share a screenshot of the Salesforce record with the record history, and Salesforce is telling them that the record update was attributed to "Marketo Sync" (let's assume that this is the name of your sync profile).
Who's right?
Technically, you both are but you need some more information to help you have this conversation with your Salesforce admin.
The reason that this is happening is that Salesforce does not have a "user" assigned to workflow actions (APEX triggers or Process Builder Flows) that are active within Salesforce that act upon record updates. Therefore, any data update that is processed from one of these Salesforce automations is attributed to the user record (in this case, "Marketo Sync") whose update initiated the trigger to fire.
This video explains this issue more fully.
This flow chart below explains the workflow at a high level:
Any fields that are updated by APEX or a Process Flow, that are tracked via Salesforce change history, will be attributed not to a Salesforce APEX/Process flow, but to Marketo Sync in this case.
What do you need to do?
First, demonstrate this knowledge of the Salesforce workflow to your Salesforce admin and present to them the evidence from your marketing automation's activity log records that demonstrate that that the update is coming via the API from Salesforce.
Second, if this is a troubleshooting case, offer to help with an audit of any APEX or Process flows that fired as a result of the Sync to Salesforce event from your automation sync. The result of this audit may require that you adjust sync behavior to avoid updating fields/data that would fire off the Salesforce triggers in question.
These two steps should help you to start to resolve any of these questions that can come up.
A word for data orchestration platforms here.
A piece of advice that I would give, especially with how interconnected these systems are and the degree to which IT or RevOps teams want to ensure that Salesforce is governed well, is to recommend that automation workflow that is updating Salesforce be outsourced from APEX/Process Flows to a third party orchestration tool for this reason. The orchestration tool will have it's own Salesforce user and as a result any updates created by workflow in that platform will be attributed to the platform itself vs. your Marketo Sync User. Some tools that you may find useful could include LeanData, OpenPrise, Traction Complete, or another orchestration vendor that meets your strategic and technical goals.