Heads--Anyone use Modern Performance???

Not understanding the big $$$$$ on core charges,Called Inertia twice but no call back,Now that get's irritating I don't care what business your in,When a customer calls interested in your product you call back--Also had to call Modern 3 times to get flow numbers that should be listed along side the heads,Flow numbers should NOT be some secret thing on heads you sell on ebay,Also Modern is on ebay and DOES NOT list the core charges and I wonder how many people push the buy now button to find out its another $1000-$1500 for core charges--Steve