Don't guess or try to make things up. Offer to get back to them with the information, and if they want it, do so. Remember that how you communicate is as important as what you communicate. Make your points clearly and briefly and don't waste the politician's time. Be Polite and Patient.
Some politicians can be incredibly frustrating at times.
They can be ignorant, insensitive, prejudiced, or even downright rude. You must resist the urge to throttle them, no matter what. Be polite and patient at all times. If you turn them against you they'll be unlikely to help your cause. Even if they refuse to help you now, remember, you or others from the movement might want to lobby them again later.