We tried in earnest to return the money to its rightful owner, but we were unsuccessful.

The people you are buying the house from can sue you for the earnest money.

ANYTHING or any amount can be used as Earnest Money as this is about the mutual contract between the contracting parties. this is the satisfaction of the seller that on what thing or money he is ready to accept as EARNEST MONEY OR DEPOSIT. this is to secure the transaction and it is the satisfaction of the seller only

He had no money or education, but he did have an earnest desire to prove himself.

I thought him a liar at the time, but now I realize that he was in earnest. (archaic)

No.