They said to him, From a very distant country your servants have come, because of the name of the LORD your God. For we have heard a report of him, and all that he did in Egypt..."
Joshua 9:9 ESV

Despite their subterfuge, the Gibeonites expressed a faith in God’s character and a desire to become part of Israel. Maybe they wouldn’t have lied if they had a complete understanding, but consider the lie of Jacob and Rebekah to ensure the inheritance of Abraham’s covenant. Jacob (Israel) lied to obtain a covenant, and so was lied to by someone else to obtain a part in that same covenant.