Pretty straight forward. I need Marketo to only convert the lead to a contact and not create an opportunity. However, it seems to do this by default. Is there a way to stop Marketo from creating the opp?
What CRM platform are you using? We use MS Dynamics and this is a two-step process. If Sales wants to run with the lead that has been assigned to them, they will first "QUALIFY" it. This automatically creates a contact from the lead in CRM. Once Sales determines that an opportunity exists, they will then CONVERT it to an opportunity.
In general, it is not a good practice to auto Convert Leads from the Marketo side, partially for this reason. I'd work with SFDC Admin to get some apex code to do what you need. Or call LeanData.