That's a beautiful bike. How old is it?
It's 5 years old. 
Is there any damage to the bike?
Nope, it's in great condition. 
Could I possibly take it on a test drive? If it's too big for you, I want to make sure it would be a nice size for me.
The frame is designed for someone 5'7" to 5'9". Does that seem like it will work for you?
It sounds perfect. Are there any warranties left on the bike or its accessories?
They are no longer under warranty, but I've never had a problem with the bike. 
Ok. Well, I'm interested. Would you accept $140?
$140 is too low for me, would $175 be feasible for you?
I actually don't have that much to put into a bike at the moment, but I could do $165, and I'll take it off of your hands with cash. How does that sound?
I could do $170 in cash. 
Ok, sounds like a deal!
Great!