They know what they want — they just haven't admitted it yet.
When you interact with someone, you can ask their player if they find you attractive and get an honest answer (usually "yes").
When you Persuade by using your considerable charms as leverage, you have advantage.
This work includes material from Stonetop by Jeremy Strandberg, published by Lampblack & Brimstone, licensed under the Creative Commons Attribution-ShareAlike 4.0 International License.