AustralianIT reports this week that for bargain hunters scouring flea markets and online auction houses for cheap mobile phones it is still very much a case of buyer beware -- even if the sellers are police.

The Australian Mobile Telecommunications Association, which keeps a register of blocked handsets, receives complaints from consumers who have unwittingly bought blocked phones from shady dealers.

However, it has been revealed to The Australian that some of those complaints are now being levelled at police auction houses.

AMTA chief executive Chris Althaus said everyone involved in the trade of secondhand mobiles should use the association's handset register.

"We've been aware that there have been auctions conducted by law enforcement that do contain (mobile) phones . . . and we've made them aware of the blocking system and we urge anyone who is going to even think about buying a phone secondhand that they should be very cautious about whether it has been blocked," Mr Althaus said.

NSW Police confirmed that it sells between 400 and 500 mobile handsets each year to help top up state revenue, but a spokesman said it was up to consumers to ensure that the phones worked.

"The property is sold as seen, with no guarantees given to its working order and no product warranty," a NSW Police spokesman said. "With any mobile phones sold it is up to the buyer to contact the phone carrier and determine if the phone is blocked and rectify this issue.

"The phone carrier is also able to contact the police to ascertain the legitimacy of the new owner and confirm it was sold at a police auction."

However, that flies against standard mobile industry practice.

The vast bulk of handsets arrive on the secondhand market after foul play or carelessness separates them from their original owners, most of whom block them in order to avoid the pain of an astronomical mobile bill racked up by a thief or discourteous stranger.

Mr Althaus said carriers would only reactivate phones without consent from their original owners in "extremely" rare circumstances. "The only person who can unblock a phone is its legal owner," Mr Althaus said. That leaves jilted consumers with two options: take the loss or tamper with the handset illegally. The latter had become a growing problem for the mobile industry, damaging its efforts to fight the trade of stolen, counterfeit and non-compliant mobile devices, Mr Althaus said.

Carriers can identify and block calls to mobile phones using their unique, 15-digit international mobile equipment identity (or IMEI) numbers. However, a phone's IMEI number can be changed illegally to match a number that hasn't been blocked. AMTA said Australia's mobile industry has witnessed a sharp increase in phones with duplicate IMEI numbers. "It's a bit like the fake Chanel handbags and Gucci luggage," Mr Althaus said. "Outside of this country there's a whole raft of manufacturers who seek to mimic and knock-off (authentic) product and they don't give a hoot about the IMEI number. They'll use any old 15-digit number."

Carriers can't block phones using duplicate IMEI numbers as they can't tell which of the handsets is legitimately entitled to use it. Last year, AMTA added an average of 475 phones to its block list per day, down from an average of 668 in 2004 when the list first began operating. Only about a quarter of those are legally reactivated. The agency receives about 10 calls a week from consumers who have purchased blocked second-hand phones.

NSW Police's spokesman said he was unable to find evidence that consumers had been sold blocked phones at police auctions.