It's odd how the ability is allowed only to target heroes, and its name is 'Select Hero', but I think it just selects units with inventories even a building xD
Maybe you uncheck (Stats - Interaction Type = Any unit w/inventory) and leave 'Targets Allowed' as Hero, try that.
If that doesn't work, then add 'Organic' to your Automatic Seller, and add (Non-organic) to your Select Hero, otherwise you have to trigger the ability for yourself
If none works, then trigger this:
When a unit starts the effect of Select hero, remove unit inventory from automatic seller, when it ends , give it to him again.
I can't think any further sorry :/