I think you misunderstand the purpose of their question.

Chinese sellers are accustomed to buyers overseas asking them to ‘fudge’ the declared value to avoid fees. Maybe it is $100 flashlight and the buyer says “please declare value of $20.”

Acebeam are asking you for this purpose. They are trying to do you a favor, albeit an unnecessary one. Since USA does not have any import fees below $800, it doesn’t matter. Just tell them to put full price. Simple.