Agent wants me to pre-walk her listings and write a punch list. Where's the line?

The report is the part that matters, and licensing definitions vary state to state, so you need to read your own state's statute or ask its inspector board before you write anything. In a fair number of states the trigger is delivering a written opinion on the condition of a residential property for compensation, and the word you print at the top of the page doesn't help you. A few states have no inspector licensing at all. That's a phone call to the board, not a forum answer, and if the statute is ambiguous it's a lawyer question.

On the second question, you already know the answer or you wouldn't have asked it. One agent supplying all 18 jobs, and the agent's interest is a clean listing. Nobody has to lean on you for the incentive to work. It works by which items you soften on the way to the page. Inspectors get twitchy about exactly this, because the whole thing they sell is that the report doesn't care who pays.

If you want to do it anyway, two changes. Contract with the seller, not the agent, even if the agent makes the introduction, and get paid by the seller. And write the scope tight: what you looked at, what you did not look at, no roof, no gas appliances lit, no opinion on remaining life. A punch list of items a buyer's inspector will probably flag is a defensible product. A condition assessment of the house is a different product with different exposure.

$300 for three hours of your time with any insurance load on top is thin. Pre-listing walkthroughs in a lot of markets run $250 to $400 and the people doing them are carrying errors and omissions premiums. Get a quote on that before you price.