It depends, obviously, but sometimes return shipping costs are too much (when factoring in original shipping costs, product cost, margins, etc), so the merchant

It depends, obviously, but sometimes return shipping costs are too much (when factoring in original shipping costs, product cost, margins, etc), so the merchant may opt to send a replacement without a return, or issue a refund without a return. I wouldn't assume this is how an issue will be handled, since it depends on the merchant and what the specific issue was. Those mattress-in-a-box things on Amazon are notorious for this. Once you get it out of the box, there is nearly zero hope of getting it back in. Shipping a full sized mattress would be very expensive due to it's irregular shape and dimensions - so I've heard even minor defects result in refunds. Ripe for abuse... so it's best to steer clear of those sorts of products unless you can absorb the loss.