And Bilam answered and said to the servants of Balak: If Balak would give me his house full of silver and gold, I could not transgress the word of Hashem my God, to do a small thing or a great one.
Midrash Tanchuma Balak 6 (via Rashi) — the house full of silver reveals his greed.
English: “His house full of silver and gold” — this teaches that he was greedy and covetous of money. He said: It is fitting that I take reward against this, for he risks his life and nullifies the will of the Omnipresent.
Character inference from the scale of the hypothetical payment.
The pious-sounding refusal is undercut by the size of the sum he names — midrash reads greed into the rhetoric of loyalty.