One of the most common coin buying mistakes is trusting the grade on slabbed coins. For the novice, a slabbed coin is a coin that has been independently authenticated and graded by a certification service. “Slab” is slang for the plastic holder the coin is sealed in. The most recognized services are PCGS and NGC. In general, coins graded by other services are usually discounted greatly because most of the coins in these slabs are over graded or have significant other problems. Many of these coins are sold on the internet or through telemarketers.
Even though a coin is properly graded in a slab, it may not have very good eye appeal due to unattractive toning, spotting, or other factors and should not be considered for purchase. Below are examples of two PCGS slabbed MS64 Morgan silver dollars. The one on the left has great eye appeal with brilliant luster. The one on the right exhibits heavy unattractive toning. Coins with extremely attractive toning can command a high premium.
So, whether you are buying ungraded (raw) coins or slabbed coins, the bottom line is that you should look at many coins before making significant buying decisions. When buying slabbed coins, always buy the coin, not the holder.