Official Canon accessories are rather overpriced but are of good quality, so buying a second LP-E8 battery for my 550D at a substantial discount on Amazon Marketplace seemed like a good idea. Unfortunately it appears that there are some counterfeit batteries doing the rounds, whether the Marketplace sellers are aware of it or not! I only received what I believed to be a genuine Canon battery upon ordering the product for the third time...
The two seemingly dodgy batteries that I received first of all did look quite reasonably convincing in their packaging, but when removing them and comparing them with the battery that came with the 550D there were some very obvious differences: the dodgy batteries were both slightly more grey than white, had a different texture, featured less well defined text (one of them tellingly had a spelling mistake on it as well!), did not feature a sticker over the indented panel on the end of the battery above and to the right of the electrical contacts, both featured the date(?) "200912" and the code "VLYA" at the bottom right of the face with the voltage and capacitance figures printed on it, and just had an outline of a triangle with a black exclamation mark printed inside it on the 'warning' face instead of a solid black triangle with the exclamation mark in white inside it.
The genuine battery looked exactly the same as the battery that came with the 550D and was presented in sealed packaging that caused some minor damage to the cardboard backing when removing the outer plastic case, whereas the case for the other two batteries had un-clipped from the cardboard without breaking a seal or causing any damage. Also, the Canon hologram on the packaging of the genuine battery had an opaque bar top and bottom with a translucent bar in the middle with Canon printed on it, whereas the dodgy batteries had 100% opaque holograms.
Hopefully these details will be useful in determining whether a genuine Canon LP-E8 battery has been delivered!