Tell him that you want to see the plugs. Sounds fishy to me. Bosch are not cheap and they are typically pretty good. I'd want to see the plugs. Check the post for wear or damage. Check for oily or greasy residue. Check the "L" (spark receiver) for damage and make sure a piston isn't smacking it. If the mech. says they are fried, I wanna' see 'em being pulled in that condition. Just me.
I'm impressed with rapid fires and ACDelco parts in general. (Do not purchase split fires. You only need one good spark, not two+ weak ones.)
For the cost of plugs, I'd purchase them just to preserve the warranty. Stripping down to the head is a P.I.T.A.!
Martin '01 Formula - MTI Air Box Lid, K&N Filter, Hurst-6, SLP Cold Air Induction & Smooth Intake Bellow Corsa Catback w/Premium Tips '83 V45 Magna