你其实并不知道listing agent (seller's agent in your word) ...

... will get FULL 6%. That's my guess. So the so-called 3% could be a moot point. I contacted the listing agent directly and bought my last condo for rental, and noticed on the transaction paper (later) that the listing agent actually only collected 1.5% as commission.

Often 6% is the "MSRP" price if you know what that is, agents don't always get that much.

Just offers a lower price and clearly inform listing agent you are on your own (with NO buyer agent). S/he should know exactly what it means.