As a fellow bookseller I get this all the time - listings deactivated for too high pricing, and as you say there are sometimes others listed at a higher price !!

They do not take into account the scarcity, or the availability, but simply compare prices across all marketplaces and expect you to be the lowest !!

Here is the policy (bold mine to accentuate the unfairness !):

Amazon marketplace fair pricing policy

Sellers are responsible for setting their own prices on Amazon marketplaces. (well that's not true for a start !) In our mission to be the world's most customer-centric company, Amazon strives to provide our customers with the largest selection, at the lowest price and fastest delivery – and sellers play an important role.

Amazon regularly monitors the prices of items in our marketplaces, including shipping costs, and compares them with other prices available to our customers. If we see pricing practices on a marketplace offer that harms customer trust, Amazon may take action, such as removing Buy Box, removing the offer, or in serious or repeated cases, suspending or terminating selling privileges.

Pricing practices that harm customer trust include, but are not limited to:

setting a reference price on a product or service that misleads customers;

setting a price on a product or service that is significantly higher than recent prices offered on or off Amazon;

selling multiple units of a product for more per unit than that of a single unit of the same product; or

setting a shipping fee on a product that is excessive. Amazon considers current public carrier rates, reasonable handling charges, as well as buyer perception when determining whether a shipping price violated our fair pricing policy.

My solution to this is to remove it from Amazon and sell elsewhere (usually Ebay !) I have had vintage, rare Ladybird books deactivated, because I was not selling at the original price of 12p !