I am still a bit confused about how a self employed person should create a valid tax receipt from a Trade Me purchase. i.e. I refer to when I BUY an item and I want proof that I have purchased it for my business. What do others do? There does not seem to be a place where I can print a tax receipt anywhere? Are the details of purchase that accompany emails sufficient?

If I see a seller who has purchased a musical instrument that I bid on and lost, and then two days later he has listed the instrument for sale for more than three times what he paid, should he be listed as a trader or just a seller? Is there a different type of listing for people who do this? Thanks for any help.