As with any form of selling, you need to focus on what the buyer
is looking for, understand his motivation and highlight the
factors which are important to them.
Are they after your location, your customer base, your product range, your distribution network, your name and reputation? Do they just want you out of the market?
The ultimate limit to the price you can get for your business is the price at which the buyer decides it would be cheaper to start up a new business in competition than to buy your business.
If you know why they wants to buy your business, and what they hope to achieve with it, you can make an estimate of this cost and work out how far you can push them.