This is something that, personally, has held me back on buying any outfits from the cash shop. Currently, there's no easy way in-game to preview them. I'd like to see what the outfit looks like on my characters before buying it. Given the "one per character per purchase" restriction on most of the cash shop stuff, it'd be a shame to buy an outfit only to find out that the look doesn't fit that character.

My suggestion would be this:

Implement an NPC somewhere that would allow you to preview these outfits like any other in a shop-like interface. You walk up to them, it pops open the list of items (or a selection box like the Calamity Salvagers) and you can right-click any outfit and hit "try on" to see what it looks like on your current character. It'd be a good way to let people make sure they're really going to enjoy the virtual outfit they're spending $8 / $15 USD on before they spend it on it.

Thanks.