Explain clearly

Govinder instructs his employee Subash to bid on his behalf at a classic car auction for a 1956 vintage Mercedes. He instructs Subash to 'in no circumstances bid more than $80,000." Subash attends the auction and successfully bids $90,000 for the Mercedes. Another bidder then offers Subash $91,000 to buy the car. Who is liable to pay the $90,000 and why? Can Subash take any action to avoid liability