Bangkok cabbie Saksri Ketsrikaew, 56, said he spent two days driving around Bangkok searching for the owner because he had no contact number.
He said he contacted community radio after he learned gold shop owner Eakerat Kanokwattana, 60, had filed a complaint with police and the story of the missing gold hit local headlines.
But police were not convinced he had a heart of gold.
"His excuse doesn't make sense if he intended to return the gold to its owner as he knew where they got off," case officer Lieutenant Colonel Udom Sukprasert told AFP.
"They are checking and counting the gold now."
Eakerat, who owns a gold shop in the city of Ubon Ratchathani, came to Bangkok with his wife to do a gold trade in Chinatown and got a taxi on Tuesday evening to the northern outskirts of Bangkok.
But he later realised he had left his bag full of gold ornaments in the taxi and offered a reward for their return.
Television news Friday showed a relieved Eakerat giving the taxi driver gold worth around $6,400 as his reward.