It could happen, and it would be flatly unethical, but treat it as an uncommon risk rather than something to assume about your deal. We have heard others describe it. We have never confirmed a case ourselves. There is a partial safeguard in the paperwork: contracts typically include a line where the seller signs to acknowledge that an offer was presented and declined, which gives some evidence the offer was actually seen. Airtight it is not. There is no clean way to prove from the outside that an offer was delivered exactly as it should have been, especially when one agent sits on both sides. Spend your energy where you have control. Chasing proof of a suspected case rarely goes anywhere and costs time you could spend finding the right home. Keep making strong offers on other properties. If you genuinely distrust a dual-agency situation, have your own agent handle the offer, or ask that your offer be submitted in a way that creates a clear record. Prevention protects you better than trying to prove what happened after the fact.