For the first:
- Do your research
- Know what you need (vs what you might want)
- Know what you can pay (conservatively, and at a maximum)
- Don't be afraid to say no
- Don't be afraid to ask questions
- Never feel pressured into a transaction - go away and think/process things
For the second:
- Don't be afraid to immediately tell them you're not interested (in fact, you should do this by default if it's something you don't need)
- Know your finances, so that you're aware of what you can and can't afford (this might be impetus to cut off the call sooner rather than later)
- If it's something you may need, or have looked at, the points above apply
An interesting thing I've discovered (anecdata) - salespeople are wary of engineers, because we rarely take something at face value. If you are one, make sure they know this early on (either state it, or make sure they know you know something about the domain). In the past it's done two things for me:
- The sales person is less likely to make wild claims, and will be more careful to make statements that can be backed up
- Often, they become less pushy, because they know they will have to work for the sale (rather than rely on emotion and ignorance)
One last comment: don't mistake courtesy for friendliness. Sales people are there to do a job. They are not your friends (you don't owe them anything), and it's the exception to the rule that they will have your best interests at heart. Keep this in mind while you're talking to them.
In my case it was the first. I did enough research and was very clear on the pricing and product, i improved on my negotiating as i visited 3 showrooms and then when i went to this 4th show room "don't mistake courtesy for friendliness" this happened and i ended up spending $2K more that i should have. He talked to me in a very nice way taking so much care about how i would like and i just gave into it as i was tired that day and already was shopping for the product for a month and just wanted to close the purchase.
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.
Hope it keeps me from falling for such traps in the future. Let me know how you managed to get out of such situations or if you had any tips to handle them.