On planets where normal sale-of-goods laws apply. If you buy a tin of beans from Tesco today for 30p, and then tomorrow you find they've got a special offer and the same beans are 20p, you don't get to take them back and re-buy them at the lower price. If you bought them, then you bought them.
If there was something fundamentally wrong with it, then of course you could return it for a refund. But if you're just trying it on, expect people to tell you fo f*ck off and stop being a dipsh*t.