I agree with binary. Sometimes ebay uses the name "tamagotchi" because they think that just stands for any kind of virtual pet. So be careful when you are buying from ebay.
Do not buy any Tamagotchis if they don't say "Tamagotchi" and if the brand isn't Bandai. Also watch out for JD, those are fakes. Tamagotchis are 15 dollars at Wal-Mart, though, if you can afford that.