How to sell your pre-owned Mobile phones ?

I want to sell my mi3 i bought in 2014 .

All the sites budli,reglobe are quoting 3-3.2 k for my mobile even it is in very good condition without scratches and any hadware issue.

quikrx not preset in my city, I post ads in olx and quikr , not so serious users offering only upto 4k max. where cn I get at-least 6k ? any online site ?