From KEH's descriptions of their condition categories:

EX "Excellent" 80-89% of the original condition. Shows moderate wear. May have small dings, pecks and slight finish wear. Glass may have some dust, but no marks.
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BGN "Bargain" 70-79% of original condition. Shows more than average wear. May have dents, dings and a goodly amount of brassing and finish loss. Glass may have marks that should not affect picture quality.
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UG "Ugly" Very rough looking. Multiple impressions in metal, excessive finish loss and brassing are likely. Glass will have marks, fungus or haze that will probably affect picture quality.

Since the lens was described as "bargain", I would think that the comments about being able to see any effect on the image quality would control. The repairman is probably correct, but, as the other poster suggested, shoot a roll and see. If you can document a problem, send it back. Otherwise, it seems like you got what you "bargained" for.