You have a unique design. You show it to a factory. Three months later, it's on Amazon for half price.
Welcome to Sourcing. Here is how to fight back.
A standard Western NDA (Non-Disclosure Agreement) is useless in China. You need an NNN Agreement (Non-Use, Non-Disclosure, Non-Circumvention), written in Chinese, enforceable in a Chinese court.
Trademarks are territorial. Your US Trademark means nothing in Guangzhou. Register your brand in China BEFORE you come to the fair.
Don't give the full blueprint to one factory.
If your product is simple (like a garlic press), it WILL be copied. Speed to market is your best protection.