API's, how pricing is calculated, scheduling (how your system knows if my shop is booked up or could use more jobs), how you curate suppliers, any non-obvious advantages to partnering, etc.
As a manufacturer, you have your own app that is used as a back office. For example, you can play around with pricing depending on how busy your shop is in a given time.
We vett supplier by working them before and taking them on a test run. Most of our suppliers are used by enterprice companies like IAI, so you can trust us that if you'll get accepted you're in a good comapny :)
In my personal opinion, the biggest advantages to partnering with us as a supplier is that we save significant amount of time on overhead (quoting, payments, communications).