Detecting Cleaned Coins
Many ebay coin auctions offer cleaned coins for sale. If a seller is honest and knowledgeable they will disclose this fact in their description. If not, then a buyer must learn to distinguish a cleaned coin from a problem free coin via the pictures and a sellers feedback. Of course, unscrupulous sellers will use lighting, reflections and angles to hide the true condition of their problem coins.

Then there is a small percentage of sellers who don't know their coins are cleaned, and sell them without this knowledge. So, it's pertinent for buyers to be as informed as possible when buying coins from any seller, until they find a few they can trust. One rule I adhere to is; If a seller doesn't respond to emails with questions or better pictures of the coins they're selling, I don't bid!

I don't trust the excuse that their pictures are the best they can take, and if this is true and their pictures leave too much to the imagination, then they have no business selling on ebay. I don't need their coins that bad with over 125,000 other US Coin auctions to chose from on ebay. If I think the seller is trying to hide or manipulate their photographs then I don't waste anymore time viewing their auction. It's just not worth my time or money to take chances.

Below I will list the different cleaning conditions you will find coins in on ebay. In this, I hope to help buyers to gain a weary eye, and not get ripped of buying cleaned coins.

Dipped: A coin that has been immersed in a substance, or had a substance placed on its surface, to removed some or all of the original or toned surface of the coin, to make the coin look lustrous. (The original surface could be grime from circulation or toning.) 

Many substances are used to "dip" coins, jewelry cleaner, bleach, Brasso, etc, and each give the coin a distinct appearance. With a little experience and a lot of caution, a buyer can learn to distinguish the differences between a "natural" coin or one that has been tampered with.

If a coin has a lot of wear and looks white, or the surface is too shiny or clean, then it may have been dipped or chemically altered. Most coins, altered in this method, will have a distinct "flat" luster due to the chemical causing microscopic etchings in the metal surface. Most normal coins will have a glossy or smooth or frosty-lustrous appearance to their surfaces. It takes a little experience to differentiate between dipped and normal coins.

Ebay poses some difficulties in identifying dipped coins, because identifying the true condition of a coin is almost impossible via pictures. Couple that with the poor photographs found on ebay, presents a challenge for any coin collector. It's recommended that beginning buyers purchase graded and authenticated coins online first, before venturing into the realm of raw coins.
Have you received a cleaned or damaged coin and the seller won't answer your emails? Report Auction Fraud

Below are some pictures of cleaned coins to give the buyer an idea of what to look for.
A coin graded by a lower tier grading company. Not only is the coin graded too high, but it obviously been cleaned. So, always buy coins in the top tier grading holders like PCGS, ICG, ANACS, NGC until you get a "feel" for what original coins should look like in pictures.
This coin was dipped, but has retoned a little. It has AU details, but the luster appears to clean and "off" to be original.
This coin is has had what is called an "old cleaning" but has retoned from storage in an album for many years. Usually retoned coins will have the appearance of a shiny luster, barely perceptible, under the toning.
An example of a obviously whizzed coin, but not all whizzed or tooled coins are this obvious. Sometimes whizzed coins will appear smooth and the fine lines can only be seen under magnification.
Whizzed (Tooled): A coin that has been polished by using a jeweler's tool, Dremel, steel wool, or a fine-wire brush. A whizzed coin will either have a mirror finish or fine lines will be evident on its surface. It doesn't have to be on the entire coin, it could just a be one small spot. Regardless, of  how much, a coin with any unnatural lines is considered a damaged and cleaned coin. Sometimes these lines can be masked with improper photographing techniques. But even the most disguised picture will have certain characteristics to look for.

One, the seller with use light glare to mask the surface details of a coin. Two, the seller may photograph the coin at a certain angle so all the coin details aren't apparent. Three: Use photo editing software to soften, smudge, or blur the cleaning lines. If you think the seller has manipulated their photos or trying to mask a coin's problems, ask for different pictures. If they offer an excuse like "these are the best I can take", then don't ever bid on their coins.
The 1904-O Morgan Dollar to the right has been dipped in a jewelry cleaner. One sign that's a give away is look around the stars and the date, usually when you see a toning outline on the design features that means the coin has been cleaned at one point. This is not a harsh cleaning and still a desirable coin that is re-toning, but it's not a problem free coin.

Also, this 1904-O is circulated despite the luster. Here's an image of an original and uncleaned 1904 Morgan Dollar.
Rubbed: Any coin that has been rubbed with either a finger (thumbing), cloth or other article in an attempt to removed contact marks on the coin's surface. This type of cleaning is the most difficult to detect, so a 10x loop or microscope should be used to detect "rubbing". Of course, online auction pictures will not allow for this careful examination. So, a buyer should always check the credibility of a seller, and always ask questions, or for better pictures.

Cleaned Coin: I added this to cover any methods that I might have missed so far in this article. A cleaned coin, is any coin that has had any of its original surface (normal circulation grime or tarnish) metal removed, all or in part, to reveal the unnatural lustrous surface underneath.

Cleaned Copper Coins: I offer a special not on copper coins. After a copper coin has been dipped or cleaned the surface will have a pale-orange hue that might look "grainy".  This pale-orange hue should not be mistaken for a the natural orange (often called "Red") luster of a mint state copper coin. You should always compare an original coin to coins you think have been cleaned.

Lasered: With the advent of laser technology becoming cheaper, many coin doctors will use them on coins to remove unsightly marks. It's not always easy detecting this type of contact mark "cleaning", but PCGS is working on eliminating this with their new technology.

Adding Metal: Adding metal to coins surface to fill in imperfections got started with gold coins that had a hole, gold metal was used to "repair" the coin. One should look at their coins with a 10x loupe and pay close attention to how the metal flowed during the strike, this metal flow can't be duplicated exactly.

I would suggest that a newbie coin collector take a handful of mint state coins with them to a dealer, or coin show, or even compare it too pictures on the computer screen. Don't be afraid to compare their coins against any suspicious coins. If a dealer get's agitated when you question their coins, go to another table or coin dealer.

Experience is the rule, rather than the exception, and until a collector has a firm understanding of coin cleaning and what cleaned coins look like, they should use every precaution before buying any coins.

The 1886 Morgan Dollar to the right has been whizzed and it's called whizzed because you can see fine lines on the surface of the coin, and it can cover the entire coin, a part of the coin and sometimes the lines can't be seen unless the coin is held at an angle under a light source. This coin is considered harshly cleaned and coins cleaned in this manner have a decreased value.