Valve could do it, only if re-sale takes place through them. What if it doesn't? Nothing mandates using some middleman for it. I.e. consider some proper DRM-fre

Valve could do it, only if re-sale takes place through them. What if it doesn't? Nothing mandates using some middleman for it. I.e. consider some proper DRM-free store like GOG. You can just copy files and charge for it directly (and then delete them, to finish the transaction). In that case, neither the store nor developers will get anything out of it.