Compare Marketo Field with SFDC Field

​Here is my question which is constantly triggering in my mind -

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​How do we compare a SFDC Field and Marketo Field automatically?

​yes, we do have sync between SFDC and Marketo, but how do we know that the Lead ID value in SFDC is same as of the value stored in Marketo Custom Field(which stores SFDC Lead ID).

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​Can anyone help me with this!

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