protect myself so that i don't give into their stories and end up buying something i don't want or end up buying something at a higher price than i had initially decided.
Set yourself a price ceiling before the call.
Develop a habit of applying a skeptical attitude towards anything you hear, especially from someone you know has motive to persuade you.
Ask to be put in touch with current clients with similar use cases to yours. Ask those contacts tough questions.
Take a couple days to "sleep on it" and consider what you've heard / research / apply critical thinking before committing to a purchase.