We almost never get offers that mention an amount. When we do, they are serious and we have sold the domain, even if the first amount is low.
When people just ask what the price is, they are being cautious, either because they don't want to spend anything, or they don't want to "offend" the seller, or both. Most of the time I ask them to let me know what they want to pay for the domain and that they can offer whatever they want. If they do, then you know what the starting point is. If they say $100 you know the end price should be nice. If they say $10, then you know they are either not going to spend much, or they are testing you to see if you reply with $20 or $2,000. Then you need to figure out how to reply, but if you are greedy they may go away. If you counter too low, you may miss out on getting what the domain is worth.
I suggest making a counter that will make you happy, but not one that will make you jump up and down with joy. If it's too high for them you can then offer a price that is "ok", but no smile. After that, then you may have to walk away.
When someone contacts you, it gives you an advantage. You know they are interested in the domain. You just need to figure out HOW interested they are and what kind of resources they have. Are they buying the domain for a big company, or are they buying for a site they want to build. Do a search in google for their email, their phone numberm and anything else you know about them. Learn as much as you can about your buyer and it may help you in making a deal.
Just don't pay for any appraisals if the buyer asks you to.
