Over 40 years in the sales world, taught me a little bit about human nature. Firm almost never means firm. Any commodity can be and will be open to a negotiation. Most people that put something up for sale, usually do want to move it. They may need the cash, they may actually not like the product, and a slew of other reasons. When I hear someone say "Firm". I actually love it. Most likely he is lousy at negotiations and even prone to giving in. Just because someone low balled your product, so what, that does not mean he might pay more, and in some cases even full boat and in some cases might even pay more than you are asking. So he took the time and he opened a door to buy. Why not listen to him. Just say, I appreciate your offer, but just out of curiosity, "Why do you think the gun should be sold at that price"? Listen to what he says and then YOU SELL your Product. Features and benefits. Sell the sizzle not the steak. Then ask him, are you really interested in this gun. Get him to start saying YES. And then go from there.
I could go on and on. but you should get the drift of what I am talking about. Have some fun with it. SELL IT! Tell why you loved it, how you cared for it, etc. And then close the deal.
When I was a very young lad in the sales world, I had a boss that had a license plate that had three letters ASK. Ask for a date, ask for a discount, ask, ask. You never know, and you will be surprised how many rewards you can get in every day life.
And here is something to remember. "Make the customer feel like he won", Even if it is a mere $10.00 off your "Firm" price.