How to find out the supplier who control the waterproof the best?

From the above blogger, we can see that the headlight needs to be IP67 to reach the grade of waterproof requirement.

How to find out the supplier who can do that？

We think it's possible to ask them to get a testing video to prove it.

Also, we can find a reliable testing company to do the product waterproof testing to prove. 

Again, we can ask our customers who use the headlight and check if it's really high quality for waterproof IP67.