Question

per the stamp act, when did tax stamps have to be applied?
when sold in stores
during inspection by an auditor
during unloading at a dock

Explanation:

The Stamp Act (1765) required tax stamps on paper goods (e.g., legal documents, newspapers) when they were sold or used. Applying stamps at the point of sale in stores aligns with the act's requirement to collect the tax as goods changed hands to consumers.

Answer:

when sold in stores