In order to keep some of your suspects out of SFDC until a certain criteria is met before syncing, you will need to change your SFDC set up.
Sounds like all gets sync on creation in Marketo. Also if adding leads to programs and that program is directly linked to a SFDC Campaign. All memebers will be synced (this sounds like your issue, that some were not ready for a sales follow up.
To help solve this, you can ask for the sales organisation to place filters on the sales views so that only qualified leads show up in their views and the lower scored leads are hidden from sales reps.
This way you have all leads/suspects synced to SFDC, some are hidden and you can still report off of your SFDC campaign reports with all memebers by progression.