Would it be a copyright infringement to include a photo of a book when placing it for sale in a classified ad?

To photograph a book to show its condition for the purpose of lawfully selling that copy is unlikely to draw an objection from the copyright...

How can I protect an idea, while trying to sell it at the same time?

You have hit upon a troublesome task. This guide from the Wall Street Journal gives a good overview of the considerations. While a television...

Can I "sell" trademarked logos by saying I'm selling an item that comes w/ free art? The art being that logo & my own designs.

First, I am unaware of any legal basis for your notion that "if something is changed by 20% then it's not illegal to use that design." Substantial...

I entered a partnership agreement with a company we both agree to put up 50/50 of the money I found out they put up no money

To really advise you, I would need to review your agreement and gain a better understanding of what has transpired. Based on what you have written...

Without knowing more facts, particularly the specific non-compete language, I would not venture to assess the risk of using ex-client testimonials...

Is it fair use to quote a post-1929 translation of a 16th century work, e.g., a modern translation of a Machiavellian quote?

A translation is a derivative work subject to copyright protection independent of the underlying foreign language original. The operative questions...