if summit or holley won't help you then you may as well disassemble it and look for whatever is causing the restriction. you may even see something from the outside blocking the idle slots at the throttle plate. perhaps they never got machined? at any rate, it sounds like some trash in there or just a screwed up carby. you could always go the dirtbag route and ebag it as-is.
plenty of scumbags sell junk there and easily claim ignorance after the fact. heck, you can just post pictures of stuff you don't even own and get people to pay for it there! the best part is ebay won't do anything but shake a virtual finger at you. 
-james
Charlie is right, by the way. Tell Summit the deal, and they may just help you out of goodwill. It would be the right thing for them to do.