This probably isn't going to help you in any way, but when I bought my corn a few months back, it was housed with another one, that was born the same month (July '06), but wasn't bigger than a hatchling. I mean really tiny. The clerk told me they didn't know what to make of it, it would eat without problems, but it just didn't grow at the same rate as the others. I obviously bought the biggest (I know it's no guarantee) of the half a dozen corns they had. Fortunately it was my favorite morph and it was also the cheapest.
Now, I'm not saying that you haven't been ripped off, but it's entirely possible that you haven't been. But of course you might have been, or possibly just been sent a problem feeder.