Fee estimation is an impossible task. There's never any guaranteed fee that will get your transaction accepted. Imagine there's 11 people waiting at a bus stop

Fee estimation is an impossible task. There's never any guaranteed fee that will get your transaction accepted. Imagine there's 11 people waiting at a bus stop, and the next bus that arrives has 10 spare seats. There's no pricing model that will allow all 11 people on to that bus, regardless of how much the people want to pay, or even how you rate the users. So it goes with bitcoin.