Finding hooks?

Hooks are only invoked with apply_filter() and do_action() or their ref_array variants. Finding the right hook in a DB can be hit and miss. The most reliable way is to trace through the code you want to affect and look for the telltale calls. This includes drilling into sub-functions through as many levels as necessary. It matters not if the code is in a class or is procedural.

It might be possible to affect WC Vendors code with a WP core hook because WC Vendors code more than likely calls WP functions which use hooks. The trick is causing your hook to be applied for the needed situation and not other situations that fire the same hook.