What to look for when buying a litho

[jlmarr]

I'm considering buying a signed and numbered lithograph by Boyer, but the seller says they don't have the Certificate of Authenticity, which in my mind reduces the collector value (resale value) quite a bit. I'm wondering what other things I should be looking for when looking for a litho:

- Creases, tears, or other physical damage

- Coming from a smoke free home

What else? For instance, what does an art dealer look for?