Always try to get them to throw out a number first. If you must go first - start high, but don't be crazy. When you deal with subjectively valued names like this, it can be a bit challenging. You really have to decide what a name is worth to you (and how much you have invested) and create a range where you won't have seller's remorse. Lots of times that range is really based on what your current financial situation is and how bad you want to sell something.
If you can Google the person and learn about who they are, why they want the name, and what kind of bankroll they might have - it can certainly help know how hard to push. If it was a huge company that made the mistake of rolling out a new service without acquiring the exact match domain first, you have some leverage. If it is a housewife wanting to start her first blog, you may need to adjust your expectations or hold onto the name.
Appraisals and sales prices are usually meaningless to a buyer unless you can show this exact name was sold or was purchased by you for a certain amount. The buyer has a range too - most domains are not "must have".
If the offer is super low, I don't even counter. I just tell them that they should look at registering something by hand, that quality aftermarket domains can't be found in that type of budget, and wish them "good luck" with their project. If they are serious, they usually come back with something more reasonable as a starting point.
