They asked me more money after payment!
They told me the seat I chose have been sold out, and I needed to upgrade. If I cancel the order, I need to pay more. However, before I payed, there was no information showed the flight I chose was not available.
In the email they sent me showed the extra money was taxes, not upgrade fee. They didn't give me a clear answer for this, but urge me to make a quick decision.
I checked the America airline office website after payment, the similar flight was only $810, which is the same price as I saw on Justairticket website. So I'm 100% sure this is a scammer website!
If you want to take a risk, use this website.