The problem there is that all Amazon stock is comingled. There isn't a difference between sold by Amazon and third-party FBA. It all gets sorted under the same UPC/SKU.

Amazon is attempting to be a physical CDN, and that's bad news when what you're looking for is a guarantee that some product will be delivered from some specific seller to you after getting comingled.

Normally, that isn't much of an issue when you've got procurement going sanely.

When it is predated by fake/damaged good sellers predominantly though is where you run into problems.