You shouldn't do it though - it is technically fraud and they will make you fill out the receipt - any decent sales assistant will check details against receipt. But these days I am sure you can get away with most things without people noticing.
some pin machines require the pin number to be input during a refund process, some don't, but before you even get that far, you should check the reciept for the ganestation returns policy for 'unwanted' or 'unsuitable' purchases, which do not come under any statutary rights to a refund or exchange.
Dotty is right, a lot of retailers these days do not offer a refund, only an exchange. Which is well within their right as long as the item is not faulty and they cannot replace it for you.
especially any type of media, like computer games, dvds and cds, if the seal is broklen you've no chance. And rightly so, they can't sell it as new can they?
They get re-wrapped and sold on if in a saleable condition Dotty. But with certain games you have to be aware of the codes you have to input to play then - like PC games, those you cannot return if opened or sell again.