What Audioguru is saying is not specific to one battery technology. Just becasue it's 'polymer' and not 'ion' makes no difference, they are both available as genuine articles of course but also both available as fakes. It isn't the battery type that matters, it is where it came from. Only use the manufacturers authorized sales agents to ensure traceability to source. I've seen 'protected boards' built in to battery packs which are nothing but a resistor to make it difficult to tell from outside there isn't something there, even if it doesn't work.
Don't underestimete the number of fakes out there, it is probably not far off the number of real ones.
Brian.