Maybe buy a big-a** cheap c-wrench of the right size. Spray on the WD 40. Let it set a spell. Wack the wrench (in the proper direction, of course) at the far end with a hammer, for maximum leverage. Lather, rinse, repeat.
If that doesn't work, find another LBS. I've bought pedals that cost less than $30.
when re-installing pedals, use some grease on the threads and don't overtighten.
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"Light it up, Popo." --Levi Leipheimer