Just fyi, doing so is actually tax fraud and very much illegal. Yes the chances of getting caught are incredibly small, but if you're doing this commercially then if caught not only you will have to pay ALL of the fees back + penalty, do it for long enough and there will be criminal charges involved.

So yes , "nobody cares" as long as you don't get caught.

Well... in my case low value on my package added a week to my delivery precisely because after seeing this trick once too many the customs are now checking everything. I had to mail the sender (big US based company) to send me the correct invoice after the customs sent me the one they received.

I think you generalize too much... do you know how every customs office work?