It's not like the shoes are going out the door without them knowing that the same person just ordered three pairs in different sizes and is almost certainly going to be returning two of them.
It's simply not possible to be sure about a shoe size sight unseen. Even within the same brand of shoe, fit varies. I have to assume a very high returns rate is totally expected by online shoe retailers (and for that matter offline ones).
Even with the fancy foot scans I frequently have to do returns because the shape of my left heel is different than the shape of my right one. The overall length and with of the shoe as well as the height of the foot fits well, but the heel counter shape can cause a lot of trouble. I tend to buy another pair in the same model and size when I find a decent shoe, but obviously this doesn't work across models and brands. Last month I did 3 returns until I found an acceptable model.
