Sometimes it’s best to just list the rules. Here we go:
When you merge two leads in Salesforce, the normal sync tells Marketo and the leads are merged automatically as people in Marketo.
Merging two people in Marketo actually invokes the same process as merging them as leads in Salesforce. It still works automatically.
Merging a lead (person) into a contact works the same way. You end up with a single contact on both sides.
When merging, the default score is summed.
NOTE
Merging 3 leads (people) with scores of 10 each, will yield a result of 1 lead (person) with a score of 30.
Conflicting field values are taken from the “winning record.” (Record = the resulting lead or contact)
If the “losing record” (the one that is disappearing) had a value and the winning record has none, we will keep the losing record. In other words, “Some value is better than no value.”