What PCGS graders look for on a coin more than anything else is an original surface. There seems to be confusion about what constitutes originality in regard to a coin's surface. Some people think it means a coin that has original toning. That's not the case.
To PCGS graders, original surfaces mean the coin looks as natural as possible. This natural look can occur in both toned and un-toned coins. To continue the example, a silver coin can be totally white and look either natural or over-dipped and washed out. The PCGS graders respond most positively to white silver coins that have natural, glowing luster and don't look like they've been dipped 20 times.
As far as toning goes, the PCGS graders look for original, natural-looking, attractive toning. A coin that looks unnatural is either going to end up with a lower grade or not graded. A toned coin that is overly dark and unattractive is not going to get a high grade no matter how original it looks. Coins that have been artificially toned will be encapsulated in a PCGS Genuine holder and assigned a PCGS No-Grade code of 91, which indicates questionable color. Genuine Not Gradable will also be indicated on the reverse of the holder.
Additionally, coins deemed to be artificially toned and are encapsulated in a PCGS Genuine holder will also be assigned a unique certification number. The PCGS certification number is located on the lower right-hand side of the PCGS label. Once you enter the certification number of a PCGS coin, the cert verification screen will provide additional details about the coin.
There is a misconception about toning. Toning can be positive, neutral or negative – it depends on what the toning looks like. In fact, most of the ultra-high grade, silver classic coins (e.g. 68 or 69) that have been graded by PCGS are toned coins. The originality of the beautiful toning on the 1881-S Morgan shown above was never in question.
There is also a misconception about both toning and copper spots on gold coins. To PCGS, a few minor copper spots are not negative. It just proves to us that the coin has probably never been dipped or played with. In an effort to get totally flashy gold coins, we think some submitters are dipping and even over-dipping a lot of their gold coins and suffering lower grades as a consequence.
The thing that PCGS graders respond most negatively to is surface haze. While it's true that some surface haze can just be flip haze acquired over the years, a lot of times surface haze is artificially added to coins. If you send a hazy-looking coin to PCGS, the most probable result will be a no grade and the next-most probable result will be a low grade.
The bottom line is, if you want to get the maximum grade possible according to PCGS standards, you should send in the most original-looking coins.