Lincolnshire Police have warned of a scam involving vouchers such as Ukash, E-Vouchers, Love2shop vouchers and others.
The e-commerce cash payment methods let consumers exchange their bank notes and coins for a voucher which represents electronic money of the same value.
This money can then be used to buy things online.
A number of recent incidents across the county have involved elderly or vulnerable people getting a phone call saying they owe some money.
The fraudsters can use a variety of stories to convince the victim that they owe money and often say they could be taken to court over the debt.
In a recent case in the Louth area an elderly man was targeted and the criminals claimed he owed £5000.
They offered that he could pay his debt early with £1,000 worth of Ukash vouchers and arranged to visit him to collect them.
The man obtained the vouchers but his bank became suspicious and the police were informed.
The fraudsters phoned the victim several times to try to get the serial numbers or codes from the vouchers.
If they had got hold of the numbers or codes, they would have been free to spend them online - without even having hold of the vouchers.
Another variation of the same theme involves fraudsters claiming their victim is owed money but must pay an administration fee to have the funds released.
One of the favourite ploys is to encourage consumers to claim compensation for miss-sold Payment Protection Insurance (PPI).
They then request the administration fee in voucher form and seek the voucher serial numbers.
Detective Inspector Andy Wardell of Skegness CID said: “These criminals are often based abroad, do not fall for their demands or fairy tales.”
“If you have no knowledge of a debt or a potential windfall then it is unlikely that one exists.”
“The old saying regularly used by police officers holds true - if something sounds too good to be true it probably is.”
“Please try to care for and advise elderly or vulnerable family members, friends or neighbours.”
“If you or anyone you know receives telephone calls similar to the ones outlined contact the police via the 101 non-emergency telephone number or call 999.”