What do I look for in a Yixing teapot?

Things to look for:
a good lid fit (twirl the lid around and see that it fits in all directions), design, composition, balance, craftsmanship (look inside the pot for poor seams from mold-made pots), pouring smoothness (no dribbles of water after you stop pouring), carburetor action on the hole in the lid (putting a finger on the lid while pouring should stop the water completely - no dribbles, no leaks, nothing, with the exception of certain styles of flat pots and pots made from textured clay), clay/firing temperature, ease of seasoning, weight, which tea you plan to brew in it, proportion in your hand, finish of the clay, sound when lid is hit lightly against the side of the pot, etc.