Only US Mint issued, modern, certified clad proof sets are included in the above values. This lists may or may not represent the highest values obtained by any clad proof sets but merely serves as a guide to their lofty premiums when graded and certified. Furthermore, uncertified (Raw) proof sets will realize a lower premium.
(Values do not include an applicable buyer's fees)
The above list is the Top Ten sold values for United States Proof Sets 1971 to date and the number one proof set on this list is the most this proof set date has ever sold for publically.
These values do not apply to raw sets or proof sets in any other holder; these values only apply to proof sets graded and certified by PCGS (Professional Coin Grading Service) or NGC (Numismatic Guarantee Corporation). Also, a few of these sets holders have CAC (Certified Acceptance Corporation) stickers and this is considered further assurance that the set is the grade and condition stated on the holder's label.
You can't buy or sell United States Proof Sets 1971 to date for the prices listed in this website unless they're in the same grading company holder, same grade, variety and condition, even then there's no guarantee your proof set will sell for the same value.
If you want to learn the value of your United States Proof Sets 1971 to date, then you must know the proof set's grade, condition, and if it's authentic. You do this by taking your proof set to a reputable coin dealer or sending your proof set to PCGS or NGC (fees do apply with these services). If you're not interested in sending your proof set to a third party grading service then you should do some research and find a reputable coin dealer instead. I recommend a PCGS Coin Dealer since at least three of their piers have to vouch for them to be a PCGS Dealer.
If you can't find a PCGS Coin Dealer then look for local ANA members or coin clubs. In the mean time you can get an idea of your US Proof Sets 1971 to date value and grade by visiting CoinHELP! website.