How do you decide a an error coin like this one? http://www.ebay.com/itm/1999-MINT-E...457?pt=LH_DefaultDomain_0&hash=item463ceae3f1 Google is my friend, coinquest says: - Post-1964 Lincoln cent struck on dime planchet: $200 uncirculated
I'm not sure of a way to put a value on something like this. I would probably start with past auction results.
Do your research. It's only worth what someone is willing to pay. Granted, it's neat but I would not spend $200.00 for it. For that money, I have numerous choices of other coins.
these often trade for 450 or more in MS grades in legitimate slabs. Research as dates are important some years and mints are very tough to find and go for a lot more even among later dates. Circulated examples go for less when you can find them. this one is in my error box of 20.