Hi, I'm interested in your seat, but I'm not sure if I'd like to pay so much for it. Why should I?
Well, it's in excellent condition due to the washable cover and the color is sure to match a wide variety of decors.  In addition, it's incredibly comfortable and durable.
I've actually had a slipcovered couch before. It was annoying and the cover always kept moving around and falling off. Will I have that problem with this? 
It moves around a little, but is securely fastened at the back of the couch.  The seat has its own individual cover.  I don't think you'll have a problem with it, we never did.
That sounds good. I'll offer you $175 for it. 
I think I could get more, but your offer seems reasonable.  I accept.