Receivers and managers have been appointed to The Rare Coin Company after 31 years of trading.
The coin and banknote dealer, based in Albany in Western Australia's Great Southern region, promised investors above average, long-term capital growth.
But the company has been placed into liquidation, with PPB Advisory assuming control of the business and securing its assets.
It's understood the company was swamped with more sellers than buyers.
Receiver and manager Simon Theobald said a detailed inventory of stock, including coins and banknotes stored on behalf of investors, was being compiled.
"We appreciate that many investors will be anxious to see their property returned to them as soon as possible, and we will be working to facilitate this in a timely manner," Mr Theobald said in a statement on Tuesday.
"However, given the volume of stock held, it is important that a thorough procedure to verify ownership and return goods be established and implemented."