Had the "pro" in GC Pro Audio up-sell me on (2) Sennheiser e835 vocal mics. They were $99 and he convinced me that they were better than the SM58 at the same price point. Admittedly, I was in a rush and needed them about an hour before a gig because "someone" forgot some of the regular mics back at the home studio, and thought what the hell, I'll try 'em.
We used them once and they were BEYOND terrible. Totally lousy frequency response, had to crank the gain ALL THE WAY UP in order to even hear the signal. Never had another mic do that.
So a few weeks after that gig I remembered that I'd meant to return them (after my anger at that show had subsided) and went back to GC. Got told by the front desk guy that, "You can't return microphones because of California's health codes".
I was stunned. I'd purchased used microphones from them earlier in the year. I even went so far to show him that they were still selling used microphones on their website. No dice.
So now I'm in the hole $200 on a pair of mediocre microphones desperately trying to unload them for practically anything on Craigslist. I'd probably give them away for a plate of tacos and a Corona!