There are lots of ways to handle these situations, which aren't unique to Events.
You first have to decide how you want to handle each of those groups:
- Existing Lead: what should happen?
- Existing Contact: what should happen?
- Net New: what should happen?
- Customer vs. Non Customer
This may also depend on things like:
- Existing rules of engagement
- What the person did at the event: Visited Booth, Scanned Only, Viewed Demo, etc.
- How you handle attribution.
- How you let Sales know a Lead (or their Account) was at the event.
- How you handle follow up.
Once those are defined, you can work out the marketo details.
they don't own the account, just the lead).
When you import into Marketo net new records, the default object that the record is created in is the lead object. In the lead object there is no relationship to the account object.
Are you saying you'd like records imported directly as contacts?