My best friend is selling an authentic Justin Bieber autograph. How much could she sell it for and where?

My best friend saw Justin Bieber a few years back (when he still had his flip hair) and her mom bought her VIP tix. She got to sit in the sound check, she got VIP seating, she got to meet the opening acts (Burnham and Jasmine V I believe her name was) as well as his back up dancers and she also got the autograph from Justin (I'm telling you all of this so you know its legit). She's not really a fan anymore and she's trying to save up her money and she figures she could sell the autograph. Where can she sell it and for how much? Also, if any of you are interested in it, let me know! Don't email me here because I NEVER check this email. Let me know in the answers and I'll just email you. Thanks guys!