That is WEIRD...I think you might have been scammed, as you can never really trust things from Ebay
Did your tamagotchi have the logo on it?
Either that, or your tama has a lot of glitches, most likely from being roughly handled by the user before you.
Have you tried resetting to fix it? Sometimes that'll work.
But, as long as you're having fun with your tama and it isn't REALLY messed up (freezes a lot, blurred screen, etc.) you can just live with it.
Also, as OldSchoolTama said, some Tamagotchis evolve early or late, so it just depends...once I had a child tamagotchi that wouldn't evolve for 4 days (this was when I was just starting to get into Tamagotchis) and it turned out the problem was I was pausing it too much, so if you pause it, try not to, because it stunts growth.
P.S. Try not to shake it, either, because Tamagotchis can be hurt by physical handling.
Hope I helped,
--*tamalover99*--