I know what the Tamagotchi looks like and i still bought a fake one, since the picture on the Ebay auction was that of the real bandai version

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My advice is to always ask the seller in front if it is a real Bandai version. Don't buy it if the seller doen't respond. Also check if the picture is taken by the seller and if the tama looks like the colours released. I've collected the available colours at
my site.
Some people can't buy Tamgotchi in their country, like me (T_T), so they have no other options than to buy it online. Here are some reliable Ebay sellers:
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Jason-
DMP88-
Jenny