The courier has minimal incentive to actually deliver to you in a timely or efficient manner.
If you count "don't piss off your customers' customers by breaking their stuff" as "minimal", then I agree. But, of course, you don't mean that. I don't think you do, anyway...
If a vendor doesn't give you a choice of carrier (and many still do) and they routinely get hit with extra costs due to a high number of returns from shipping damage, then you bet they're going to tell the problem courier to fix the issue or move along. There is *absolutely* incentive to deliver in a timely and efficient (and intact) manner. The couriers will lose business from their customers, even if it's not you.