If you sell villagers too many boards, loop snares, or pretty much too much of anything, they stop accepting this item in trades and say "no thanks, we don't need more X".
However they don't consider this limit at all if this is the first trade done using this material. So it's possible to e.g. gather 300 boards, take all tradeable items from the entire village, and trade them all for those 300 boards in one huge barter. Afterwards they will of course not accept boards in any future barters, but this first massive barter will always go through.
I believe this is an unintended exploit, and it would be more reasonable if even in the first trade villagers already enforced some limits like "we don't need this many X, we can accept 20 of them for this trade, but the rest of this trade you must pay in some other items".