[Armin]

I can't even fathom how commerce would work without extensive magic. Human coins would be too huge for faeries to use, and too tiny for titans to use.

With extensive magic, either every coin is a magic item that sizes itself, or perhaps everyone uses counter checks written on resizing paper.

Unless people tend only to deal with others of similar sizes. Faeries only do daily commerce with Faeries, titans with titans. The middle groups can probably get by with human sized coins. Faeries and titans could deal in bulk from the mid-folks, where transactions would be in large enough quantities for larger coins/bars to work, or banker-level transactions.

There's a lot of issues the more you think about the situation. Groups that cohabitate but don't interact much is much easier to comprehend.