Maybe the people at the tire shop are flippin idiots?

If they're giving two diff. tires with diff. PSI ratings, then chances are they're also lazy/stupid enough to not pay attention to giving you... say, one normal tire, and one directional tire that's on backwards? Etc??

I'd try my best to get your money back or something because it sounds like they tried to fuck you in the first place....

for $300, you wouldn't have been far off from a decent set of ES100's or something anyways...