It is very easy to create fake accounts which appear real to a superficial check. The usual method is to use TOR so if Anker wanted to remove fakes they'd have to cross-reference in real-time each post with the current TOR exit addresses (which keep changing).
The effort vs reward given its only some $20 earbuds isn't worthwhile but if someone just wanted to do it for its own sake its not difficult.
Where Anker could get clever is that the TOR exit address does not match the general location for shipping of the prize. e.g a TOR address in say Italy but a shipping address in say Canada. But then Anker would have to put in the effort to look for such anomolies. Also the same shipping address in each competition for different aliases is also a way to spot an individual using these methods.
Now then, so the limiting factor is therefore how sophisticated is Anker. So if Anker did what you wanted for of show the fakes, you can infer how Anker does it and keep one step ahead.