Hello
Hey there! I'm interested in your phone for sale. Why are you selling it?
I have my own and am looking for someone who is looking for a phone that is in excellent condition. 
I'm interested, but $650 is what AT&T charges for the phone new from the store. For that price I get a warranty and know for sure that it's never been dropped, used, stolen, etc. Would you consider selling it for $400? I checked online and that seems to be the going rate.
That might be a bit too low. Would you be willing to pay 500 dollars for it?
Do you have any accessories that you could include?
Yes, the charger comes free and also a protective case. I wil throw that in for free as well.
I get a charger if I buy it new! If you throw in a nice case I'd raise my offer to $420. Would you happen to have any extra SD cards laying around? I have a ton of music and could use some extra storage!
Yes, and I will throw that in for free as well. So, do we have a deal? 500 dollars.
If you throw in a case and SD card I'll do $450.
Even better. I will do that. 450. Is it a deal?
Sounds good!