Scammers have made away with more than $140,000 in at least 173 "mixed delivery order" scams that were reported between July and October this year, the police said on Wednesday.

This is compared to 26 cases that were reported for the whole of last year.

In an advisory, the police urged consumers to remain vigilant when purchasing objects online, by only doing business with people they knew and trusted. They should also check the track record of the company and seller.

In such "mixed delivery order" cases, victims fail to receive goods that they bought online, and are also cheated into wiring more money before they realise the scam. Culprits tend to post online advertisements of the sale of smartphones, tablet computers, laptops and bicycles on popular websites and Facebook below market prices.

Interested parties will then be asked to make payments through inter-bank transfers for local accounts, or to remit payment to overseas accounts.

Victims will then be cheated into making further payments through false notifications that the package was either held or wrongly delivered to another country, seized at customs, facing courier or shipment problems, or was not of sufficient weight and thus required more orders.

To avoid detection, the culprits recruited money mules - intermediaries which receive payment from victims and then transfer proceeds to the culprits - who were enticed by potential business opportunities or romantic relationships.

"Over time, trust is gained and the mules are convinced to assist in the culprits' purported businesses by making bank fund transfers," the police said in the statement, adding that the culprits may also use pre-paid SIM cards with local phone numbers to facilitate the scam.