It's like a letter to Santa.
On Toyhouse, basically people have a list of preferences for art or designs. This could include favorite artists/designers, favorite species, color schemes, themes (like futuristic/fantasy/etc), or whatnot. If they're entertaining trades, you can see if you'd have something they'd like by checking out their preference lists.
If they're looking for art, they might specify favorite styles, topics, things like chibis or fullbodies or couple art.