Unemployed people and low-income families wanting extra cash for Christmas are being targeted in bogus advertisements.
They are being offered the chance to earn money for assembly and packing work at home - but they have to pay first.
The West Yorkshire Homeworking Unit says many cash-strapped people could end up losing money by answering the adverts in the run up to Christmas.
Home-working co-ordinator Chris Love said: "These schemes are there all year round but people's need for money might be particularly pressing now at Christmas time. Our main message to them is that you should not have to pay money for working at home."
The adverts appear in shop windows and newspapers, on lampposts, or in leaflets through the door and offer excellent rates of pay for assembling or packing items at home.
"The first warning sign is when the advert asks you to send a stamped-addressed envelope to an address outside the area - often to a PO Box number," she said.
"This is followed by a request for a deposit or a fee for registration or administration, postage and other "costs"."
The problems start when the home worker returns the items they have packed or assembled.
"The work is never good enough - it never meets their quality control standards so you end up losing your fee and not getting paid," she said.
Another scam asks for money to provide a register of homework schemes and employers.
"No-one to the best of our knowledge has a register of employers because genuine home work is difficult to find," she said.
Unemployed Lyn Britton says she has lost £70 trying to get home work after answering an advert in a Bradford Post Office window.
"I sent off two lots of £15 to get booklets listing people offering home work," she said.
"Then I had to send off £40 for the particular job I wanted to do - sewing buttons on to a card. I did one and sent it back but they said it wasn't good enough.
"I asked them to send it back so I could see what was wrong but they didn't and they said they wouldn't refund my money either.
"I really thought I would be able to make some money - but I ended up losing it and having to borrow from my dad."
The 33-year-old from Little Horton Green, who has been out of work for a year, said: "I eventually went to their address in Wetherby and it was an empty office with a desk and a phone.
"I would never do it again and I would advise anyone else to leave these adverts alone."
West Yorkshire Trading Standards officers say it is difficult to prove the schemes are breaking any laws because of the way they operate.
A spokesman said: "The main thing to remember is they are asking you for money up front and you are unlikely to make any yourself."
The West Yorkshire Home Working Unit offers advice on how to find home work and can be contacted on Freephone 0500 296699.
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