After successfully defeating a raid the villagers all have discounts for you when you get the "Hero of the Village" effect, but they still require you to have the original amount of the thing they want you to sell to them. I.E. if they originally wanted 16 carrots and the discount bring it down to 10 carrots, you will have to provide 16 carrots but they will only take 10.

Confirmed in newest snapshot.

edited again: they now require and TAKE the full, original, amount for the trade.