At the general settings tab, you can setup the overall settings regarding how shipping methods are handled, especially regarding vendors.
The shipping method settings section:

This section allows you to set up, how shipping methods are handled for vendors.
The following options are available:
| Field | Description |
|---|---|
| Shipping Method Selection | Set the way, shipping methods are selected during checkout. Vendor shipping methods: Only vendor and product level methods will be used for vendors Global shipping methods: Only global and product level methods will be used for vendors Global and Vendor shipping methods: Global and vendor and product level methods will be used for vendors Only product level methods: Only product level methods will be used for vendors Global Shipping Methods (Vendor Selectable): Only global and product level methods will be used for vendors; Vendors can opt out from methods at the storefront admin area |
Depending on your settings, only certain shipping methods are available for vendors.