The Gibeonites' deception of Joshua.
Israel is deceived because they do not consult with God.
Gibeon is like Rahab: Gentiles who believe what they hear about God, and so they seek protection in unusual (immoral?) ways. They are the only ones who receive mercy from God in Canaan.
Later, Gibeon is still part of Israel. Israel is punished when Saul kills many Gibeonites, against this oath of protection (2 Samuel 21:1). The tabernacle is put in Gibeon later, since that is where the water and wood carriers are (1 Chron. 16:39; 21:29). David has a Gibeonite as a mighty man. Gibeonites are listed returning with Israel from exile, counted among Israel's number (Neh 7:25). They are not despised and hated down the generations for their deception in Joshua 9, but received as God's people (2 Sam 21; 1 Chron. 8:32).
Psalm 15:4 - He who swears to his own hurt can stand before God. Joshua keeps his oath in God's name. Their loyalty to their oath, and obedience to God (Joshua 10:6-8), redeems their mistake and solidifies Gibeon as included in Israel.
We have an oath from God Himself on which to rely for our protection. The Gibeonites were saved, though they deceived Israel, and though they depended on a human oath. How much more are we saved when we trust God's oath to us. Read Hebrews 6:13-20!