Albert Barnes Commentary Numbers 23:4

"And God met Balaam: and he said unto him, I have prepared the seven altars, and I have offered up a bullock and a ram on every altar." — Numbers 23:4 (ASV)

God met Balaam - God served His own purposes through the arts of Balaam, and manifested His will through the agencies employed to seek it, dealing in this way with Balaam in an exceptional manner. To God’s own people auguries were forbidden (Leviticus 19:26).

I have prepared seven altars - And therefore Balaam expected that God on His part would do what was desired by the donor; note.