I always though the hardware was the same and only the software changed(?) Here's a reference-
http://en.wikipedia.org/wiki/IPod_Touch#Comparisons_to_the_iPhone_and_model_comparisons
If you have any issues with the point of sale go there to clarify what traspired. It's normally much more difficult to deal with the big box stores via phone than in person IME. Print out the kb from the apple support pages & also bring in the wikipedia printout so all parties are clear on the various specs. I certainly wouldn't count best buy as place where their hourly employees are particular astute at knowing the subtle differences between devices.
I bought a iPod touch

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