Several years ago, I bought an error coin in my series from a top dealer at a major show. It's an uncommon error (split before strike), 150 years old, in a reputable TPG
Like all errors, it's essentially unique, and difficult to price. I paid pretty good money for it, but both parties thought it a fair transaction.
I love the coin, I did a huge stackshot of it and have it as a 12x12 image at my desk at work and on a 30x40" poster.
Couple months back, I cherrypicked another, similar, maybe even better one on eBay, raw. This one split so that the date is visible, not just the edge of the rim (and yeah, if you search here at CCF you'll find both posted - the specifics of the coin aren't relevant to the question).
The question: I plan to be bringing it to NGC at the ANA
show... but I will have to put a value on it for the return insurance. Do I use what I paid 3 or 4 years ago? More? I'm definitely not using what I paid on eBay this fall.