What a great idea Ebay offers are - I can put up an item for sale at the amount I would like to get, you can make me an offer for the amount you want to pay.  The downsides are, I don't get to see your email or user ID so I cannot communicate with you, and the offers happen in real time, so offers made close to the end of a listing may get lost just because I'm not around to handle them.  If you want to make me an offer, why not "ask seller a question" at the same time - it gives me the option of getting back to you.  Also worth remembering that if the item is new, I had to buy it in the first place and I keep my prices pretty low to start with - so offering 20% of the purchase price (as has happened rather too often recently) is a guarantee of a refusal (UNLESS I'm seriously desperate to clear the shelf, at which point I'm more likely to put it up for auction!)