so I've been wanting a black rifle of some sort for a while now and had planned on going the cheapest route possible by buying parts and building a custom rifle. Well, I just found out a friend of mine is owed cash by a former boss and the boss doesn't have any cash... but he does have a bushmaster AR15. So my friend will most likely end up with the AR as payment and he wants to get rid of it. He is offering it to me for $700, payable over time and he will give me the rifle as soon as he gets it

since he has no place to shoot it or store it and is too broke to buy ammo for it.
I'm trying to figure out if it's worth the $700 and I know virtually nothing about ARs. All I know is it's a lightly used, good condition, bone stock bushmaster .223/5.56 AR15 with a standard, non-telescoping stock. I don't know the exact model, sights, mags or barrel length. I have not seen the rifle yet.
What I want to know is what to look for to help me decide if I should take it or not. Thanks!