If your packages are really being opened as often as you say then you are likely on some sort of list. Having received "thousands" (!) of packages from Asia might have something to do with it - that is well into what most people would consider commercial quantities and they have possibly flagged you as potentially running some sort of unlicensed import operation.
I can confirm that in my country (Australia) packages are rarely opened and if they are, it's seldom for duty assessment but checking for contraband of whatever nature. Even if they do flag you for a duty check they don't need to open the package - they do have x-rays, you know. Try and declare a $10,000 drone as a package of t-shirts worth $5 and the officer doesn't need to open the box to reject your "estimate". That said, most sites of any repute worth upholding will print the real value on the declaration, non-negotiable.
I can confirm that in my country (Australia) packages are rarely opened and if they are, it's seldom for duty assessment but checking for contraband of whatever nature. Even if they do flag you for a duty check they don't need to open the package - they do have x-rays, you know. Try and declare a $10,000 drone as a package of t-shirts worth $5 and the officer doesn't need to open the box to reject your "estimate". That said, most sites of any repute worth upholding will print the real value on the declaration, non-negotiable.