You can set them to load/unload specifically.

Autotrade has no settings you can set that I'm aware of. I'm talking about autotrade, not trade routes. If there is a place where you can set settings for autotrade, I'd like to hear about it.

I'm trying to find if autotrade does this so I don't have to set a trade route. I don't want my traders sitting around doing nothing or hauling half-empty holds when there isn't enough to load.

Expectation:
Autotrader ships would look for the best deals.
The check mark on stations would effect if that material is traded there.
If your ships are autotrading with your stations there shouldn't be an exchange of credits.

'Best deal' would likely lead them to gather at your stations for 0 cost to sell for a profit but would preclude them from buying at a cost to bring to your stations for 0 profit.

Result: ?

Whether any of that is accurate to the game I can't say. If they are loading from your station you have no control over where they take it. Likewise if a trader drops off at your station you have no control if it was produced by you or bought from another company.

If you do want that control use trade routes instead.