In perusing various listings on eBay I noticed that many of the pictured slabs have part of the barcode or number above or below it blurred / blacked out- does anyone know why?
Not sure I quite understand- do you mean that it is done to prevent someone from tracking the coin based on the number? If so, why is that a bad thing? Or, what am I missing?
AgCollector, Many of the sellers do this if they have more than one of the item. They use a stock photo. This way you will not be able to say whether or not the coin in the picture is the acutal one you won in the auction. Some sellers will mention it is a stock photo in their auction discription somewhere usually. Other's such as e-Bay's famous ABONCOM and their SGS modern coins will always have their numbers obscured.
The only two reasons I can think of is (1) that you will not receive the coin in the photo, or (2) the seller obtained the coin from dubious sources and might suspect that it was stolen.
What the others mentioned are likely reasons for blocking the serial numbers and barcode. But what gx said is valid as well. By capturing the pics from ebay or any other source, along with the serial numbers and barcode it is possible to create an extensive pictorial database of coins slabbed by various companies. But to do so you would have to use other people's pictures. Such a database could have many uses, not all of them good. So some folks may block the numbers for that reason.
