I just inherited a .54 T/C Renegade flintlock in near mint condition. Never even been fired. It was dusty from being stored in the back of a closet all these years and I needed to replace a screw but other than that it was like brand new.
I was told that it's worth over $500, depending on market conditions.
A lot of people won't buy flintlocks because they don't understand them. That's how I came into the one I got. My step dad got it from a guy who won it in a gun raffle but couldn't wrap his brain around how to fire a flinter. So the guy sold it cheap. My step dad gave it to me because he's already got a flintlock and he's got it shooting just the way he likes. Before he gave it to me, it was just sitting in the back of the closet, collecting dust.
The bottom line is that your gun could be worth $1,000,000.00 but if nobody is willing to pay that much, what's it REALLY worth?
If the gun is sound, if it has all its parts, if it's not scratched up or rusty and it's safe to shoot, $200 probably isn't a bad price.
Do you know somebody knowledgeable enough to tell if the gun is in safe condition? If not, you might be able to convince the guy to let you take it to a gunsmith.
If you were selling a used car, you'd allow a potential buyer to have his mechanic take a look at it. Wouldn't you? Same goes for guns. Right?