If there is one sure method of lowering the value of your rare coins, it is to clean them. Cleaning your coins will generally reduce their value by 80% to 90%, because coin collectors value the original, pristine surfaces of their coins. Even a tarnished, grimy-looking coin is preferred over one that has been improperly cleaned. Being able to tell if a coin you want to buy has been cleaned is an important skill to have. Although reputable grading services such as NGC and PCGS claim they don't slab cleaned coins, mistakes do happen, so you should learn to tell the difference between a coin with original surfaces and one that has suffered the indignity of being damaged by "cleaning."

• How to Tell if a Coin Has Been Cleaned

Mike Byers has published another excellent edition of his free Mint Error News Magazine. The current issue is cram-packed with more than 250 pages full of information and photos relating to error coins. As always, Al Levy's error coin price charts are fascinating. For instance, we learn that a blank Monroe Presidential Dollar with edge lettering sold for a whopping $20,000 on eBay! Another specimen of basically the same thing sold a little later for $1,791.67. Both were in NGC holders with no grade given (as is currently customary for NGC when grading blank planchets.)

Other pricing information I noted was that plain edge Washington Dollars (remember those?) are selling for an average of $43.85 raw on eBay, with graded specimens up to MS-64 running from about $60 to $90 depending on who slabbed it. MS-65 and 66's in PCGS and NGC holders were selling for about $80 to about $150.

I've had my eye on the Wisconsin Extra Leaf Quarters on eBay for awhile now, meaning to pick up a pair of them for my collection while prices are at their all-time lowest for these fascinating varieties. I pounced about 3 weeks ago, paying Read more...