I'll come and pick them up from you for $50
Come on that's way too low. Can you make a reasonable offer? 
I was told to ask for $50. They are used, correct? 
Yes these are used but even used ones are worth much more than 50. Other used ones in worse condition are selling for 150. Can you do 95?
How about we meet halfway. How's $75
I can't meet you halfway since you started so low. That wouldn't be fair at all. I actually already lowered the price to 100 in the first place. So how about 90 and we have a deal.