Let me clarify.
When you attempt to buy something in the ToriExchange, you're placing an order for an item of that type at a cost. That doesn't mean to say that an item is actually being sold at that price.
When or if someone starts selling the item you want for the price you've specified or cheaper, they'll get your credits and you'll get their item in your portfolio.
If you don't want to wait/want your money back, just cancel the order and you should get your credits back.