Comment by LeifCarrotson

You've described a load cell, which is commonly used in laboratory and industrial environments to resolutions exceeding 0.05% of full scale. I've used these in the past with great success:

https://www.interfaceforce.com/products/load-cells/low-profi...

Click the "Specifications" tab to see the various error sources. Interface's technical library (linked at the top right of their shop) is a great training tool too, if you want to learn more. To keep your NIST certification - and to maintain accuracy after a high-stress...incident... you need to do occasional recalibration. That would be a problem for a consumer product, but with good mounting and overload protection they really don't change that much over time.

Then you've got the electronics, and the amplifier required to get the rated precision out of that load cell costs more than the load cell itself.

Achieving those performance targets costs money, and people buy the cheapest scale that says "Accurate High Precision Digital Bathroom Scale Glass" on the Amazon listing.