This is not a glitch in the plugin! This is part of the normal Amazon API functionality.
Here is the official word from Amazon on why that happens:
Some manufacturers have a minimum advertised price (MAP) that can be displayed on Amazon’s retail website. When the Amazon price is lower than the MAP, the manufacturer does not allow the price to be shown until the customer takes further action, such as placing the item in their shopping cart, or in some cases, proceeding to the final checkout stage.
When performing an
ItemLookupoperation in these cases, the string “Too Low to Display” is returned instead of the actual price. Customers need to go to Amazon to see the price on the retail website, but won’t be required to purchase the product.
Now, that does not make it anymore acceptable, but that is why it happens.
What can you do? Nothing at the moment. BUT, we are working on a workaround to add to the plugin that will return the first offer price if there are multiple sellers. Usually the fist one is the actual main seller anyway, so we hope to be able to return at least a price if there is one. We should have it ready VERY soon.