For a private seller I will tell them the true value certainly, and pay them a fair price for it, and I have done so.
I did have one instance I've mentioned before where a local antiques dealer had a large watchmaker's cabinet I wanted to buy. Nice old wooden cabinet that I wanted to use for it's original purpose, but he wanted "antiques" money for it, so no deal on that.
The drawers were all full of various parts, and he wanted me to buy the parts by the drawer. Went through them all, found several that I was interested in, and asked him the price - far too much for what the parts were actually worth. I didn't pick a drawer full of small rectangular glass crystals, and he said how surprised he was because the watchmakers in Toronto would snap this up in no time. This told me he clearly had watchmaker connections. I also passed on a bunch of rusty balance staffs he wanted top dollar for, so he wasn't giving anything away let's say.
I closed a bunch of drawers and left the one with a bunch of partial Omega movements open, and asked if I could break his "buy by the drawer only" rule by moving one item from another drawer and adding it in. He said it would depend on the item, so I moved it and he said "That? Yes fine, no problems at all!" and took my money. I'm sure at that point he thought he had fooled me or something...
What I added to the drawer was this:
Partial Laco WWII pilot watch, missing the balance, hands, and case. I really wasn't sure what it was worth, but I knew it had to have some value. I ended up selling it to a watchmaker in the UK who specializes in restoring these to use for parts, and it paid for the entire purchase I made that day. It was a gable on my part, but I certainly didn't feel bad about it after.
Not something easily valued I think, and for all I know I sold it far too cheaply also, but I was happy with what I received for it.
