Why Norway did not simply inspect Altmark

Why could Altmark remain in Norwegian waters after refusing inspection?

Its state-ship claim made inspection diplomatically fraught, and Norway tried to preserve neutrality by moving it through rather than forcing a confrontation.

Altmark claimed protections comparable to a warship while seeking passage on terms associated with a merchant vessel. Forcing an inspection risked a confrontation with Germany, while expelling the ship would expose it to the waiting Royal Navy. Tank-Nielsen wanted Norway to follow its neutrality rules strictly, whereas higher authorities preferred to move the ship onward without establishing what was aboard. The criticism of that policy is that either belligerent could use the outcome to challenge Norwegian neutrality. Britain and Germany both had invasion plans, so allowing Altmark to escape through Norwegian waters offered no assurance of safety. The alternative proposed is firm enforcement backed by mobilization and sufficient spending on the armed forces.