I typically look for original villagers, though I can do without the original shirt/clothing as they will eventually change either by themselves or from trading with other villagers. Why do I want original houses? Because there is usually an item I want or I really like the aesthetics of the room. For Marshal's home, I wanted an original house because his sloppy furniture is nearly impossible to get in the game (of course it's easier now that you have TBT retail forum, dupes, hacks, etc), but why pay for his furniture when his house already comes with it?
Anyways, everyone has their own way of playing AC:NL which is why it appeals to a wide audience range. As for why it may seem difficult to sell your Marshal, it may be for the reasons stated by another forum member. Most villagers can be purchased for lower and most of them original, however understandably this is your thread and how much you're looking for is totally up to you.
But just wanted to input my two cents. Hope your Marshal finds a good home!