You can give them your Unsubscribe Page URL from the page in Design Studio, if you use that. Or the appropriate link to your subscription center.
When I deal with list vendors like this, I always give them the following list, just emails only:
-Email Invalid = True
-anyone else who should be suppressed, such as Competitors, Current Customers, etc.
You need to build these smart lists in the Lead Database using the appropriate filters for your system. You can start with the first two filters.
Then Export All Leads with just email address to XLS. It may take a while to download. Be sure to check that you only send them the minimum information (eg: email address) in the final file.