Got hit with a 10 EUR clearance fee recently. This fee seems to be
some kind of widespread scam. Have clearance fees been challenged in
court?

For those hearing this for the first time, a clearance fee is an
additional shipping/handling charge imposed by a private 3rd party on
*recipients* of a delivery. This fee is above and beyond the
(prepaid, fixed) s/h contract that was originally agreed, and also
apart from VAT.

The rationale is that an EU customs agency might randomly inspect your
package to assess VAT (which is of course legitimate). But then the
private company who was subcontracted by USPS (for example) to finish
the delivery within the destination region is apparently not paid in
full by USPS. Instead of actually delivering the package, they hold
the package as collateral until the recipient appears in person to pay
them an additional 10 EUR to compensate them for the burdon of putting
the package through customs. The 10 EUR clearance fee is *not* duties
or VAT, and it varies from one courier to another. It's often bundled
together with the VAT and itemized as "Duties and fees..." to hide
what they're doing.

Has anyone tried to reject the package in these cases?

As I see it, the seller did not deliver. There is usually no
indication on the invoice that the s/h fee is *partial*, so it seems
the sellers are at fault for not executing the contract as agreed.