Before I ever knew the word polyamory I just would tell straight up " I like you. I want to date you. But I'm not looking for anything exclusive. What are you looking for?"
It's part of the whole dating thing and getting on the same page.
It's much easier to part on a good note if they go at the very start "Oh, but I AM looking for exclusive. This won't work."
Then we can just be friends or not friends. But without hard feelings of "You never SAID! At the beginning your never SAID! That's lies of omission! "