The Adelaide man's penchant for coin collecting began after he couldn't find a 5c coin dating back to 1972.

She'd checked out car washes, coin collecting, gardening, but she really knew so little about her tenant that no other terms had come to mind.

Earlier this year, a $1 coin made the news after it was listed on a coin collecting website for $4000, because of a minting mistake.

The highest price the coins have sold for, according to The Australian Coin Collecting Blog, was $2742.75 in 2016.