how to i preview a head without buying the texture?
if i can do that

Actually, you can.
You need to save your head texture as head.tga in your Toribash folder, custom, Test (if you want to try the textures on "Test").

Then, open Toribash, type /lp 1 Test and you should be able to see the head texture.

You should find a better tutorial in the Tutorial Board.