I don't think that it is correct blanket advice to size down on loafers. Loafers are less forgiving than bals or bluchers because laces can be the adjustment of fit for these two. Get your loafers a bit too large and they are slipping on your foot and/or gapping on the sides.
So the answer is Get the right size. Whether you must size down is something to be determined on a case by case basis.
I'm ordering online. What do you suggest I do? (Ferragamo)
Find a place that carries them and try them on. I won't buy loafers online because the fit is so tricky (having written that, I usually size down 1/2 size for penny loafers, but not for monkstraps). I learned this after returning several pairs of loafers because the footbed was too shallow for my foot.