Hello, I'm interested in buying the bike.  I am short on cash, but I really like the bike.  Can I buy it for $125?
I can't do $125.  I can do $165 if that will help you out. 
What if I throw in my old bike.  You could sell it too.  That bike should be worth about $50 or $60.  So I would pay you $125 plus my old bike.  Do we have a deal?
I am really looking to get the cash for this bike, and don't have time to sell another one. How about we make a deal at $155? 
I can pay $150.  Do we have a deal?
Yes