Hello there, i'm very interested in the device, but I'm not sure I can afford it. Would you be willing to accept a lower offer?
Hi there! Yes I am open to negotiating :) 
I'm assuming this phone doesn't have any damage as you state it is relatively new. It's in good working order then?
Yes it is absolutely in a good working condition and has no scratches or anything. It was always used with the cover and its as new. 
Great, well I'm a bit strapped for cash, so how about $25 in cash.
Woah! That's too too low. I am selling it for 70$. I can go up to $65
I wouldn't have enough money left over for other things at that price. Could you take $40
I can take $50 
Fine will go with $45 but I will give you without the cover then!
Ok