How much do you weigh? I have heard of this only with riders around 300 lbs. I was 210 lbs when I bought mine and I cannot imagine it pancaking like you mention. It is hard as a rock initally and 300 miles shouldn't crush it. Perhaps yours was defective. I would still try to return it. Just because you bought it on ebay doesn't mean you are stuck with it. If you are less than 250 lbs, there is clearly something wrong with that saddle. Even so, try to return it.