In the past, on occasion, I have bought the same style show in two sizes, trying both on side by side, and deciding which fits best.
This is in such cases where I cannot first find the show to try on locally. I say that as even though I keep to the same brand show, some styles do run slightly differently than others.
So on this case I know I'll have to spend money to return one of the pairs, but it is worth the peace of mind to me.