Concern about Duplicate lead creation

[Anonymous]

We have a scenario , where we create a lead in marketo using webservice API. Later on the same lead gets synced in to marketof rom salesforce.
I wanted to know if this action will-
1. create two different leads
2. Merge these leads

the source for first lead will be "WebService API"  and the one coming form salesforce will be "marketing".

what will happen to source once we merge this?  Do we need t update the camapaign to include lead from both sources?

Thanks,
Neha

[Anonymous]

You could push the net-new upsert via the API into a Lead Queue in SFDC. This would solve the dupe issue...