As others have said it is not worth that much. My guess is you cna put it on a gu shop shelf for about $1,400 and it will sell pretty quick, You will get about 70 to 75% of that as a consigned item and about 1/2 of the 1400 being sold out right to the shop.
I have done this with a buddy of mine a few times for a friend of mine where he hands me a gun till he can pay me back.
I guess the questions are;
1) how reliable is he to pay you back
2) is the friendship worth loosing if you sell his AR after a certain time
3) what are the laws in your state, could you be charged with illegally running a Pawn shop or selling stolen property if you sell it with out his permission? ( I had a friend, repeat HAD a friend in college that owed me money and he handed me a shotgun to be fixed, after about three years of him not making a payment on what he owed me or paying for the parts I put into his shotgun to fix it, I told him if he did not pay me I was going to sell the shotgun, he had the DA of Norfolk call me and tell me if I sold the gun he would charge me with extortion. Had to send the gun back to him and have never been paid)