Suppose you are a newly-elected parliament member. You want to faithfully represent your voters, so you want to ask for their opinion on issues discussed in the parliament. If you are in a regional voting system, you can just poll the voters in your region. But if you are in a party-list system, how would you know who your party's voters are? You could try to make a poll among the voters of your party, but then voters of other parties might lie and say that they voted for your party, in order to influence your vote in the parliament.
What are some ways by which a parliament member in a party-list system poll their voters, such that they faithfully represent their opinion in the parliament?