Work-at-home scams which lure people in by promising thousands of dollars a week for just a few hours work aren't just proliferating in the down economy. They're also getting tougher to distinguish from legitimate employment offers.

For the millions scouring web sites and newspapers looking for work at 8.5%, unemployment is at a 25-year high the pressure to find income can cloud better judgment, making scams even harder to detect. There s such desperation among a lot of people to find a legitimate way to make some money, says Tory Johnson, CEO of Women for Hire, a New York-based employment company.

Monster warns its users against such job opportunities here. CareerBuilder talks about work-at-home scams here

There are plenty of red flags that can help you recognize a work-at-home scam. If an ad promises big earnings for a few hours work, with little or no experience required, it s likely not legit. Many of those scams also try to create a sense of urgency, telling you that you only have a certain number of days if not hours to respond, or there are a limited number of positions left. It s a tactic borrowed from infomercials that isn't used by real recruiters, Johnson says. Demanding a large upfront fee or asking for your bank account number should also raise your guard.

Here are five work-at-home schemes that can be difficult to distinguish from a legitimate employment opportunity.

Rebate processing

We ve all sent in for a rebate or two at some point, so processing rebate forms at home sounds like a believable albeit tedious opportunity. In reality, very few such offers are legitimate, says Christine Durst, CEO of Staffcentrix, a firm that provides virtual-careers training to the U.S. Department of State and the Armed Forces. "Only a couple of companies actually do process rebates and they require that you live within a certain radius of the company because you have to do pick-up and drop-off, she says.

The opportunities advertised, meanwhile, usually turn out to have very little to do with rebate processing. Once you pay the upfront fee typically around $200 you're likely to be told that you have to start your own web site and become an affiliate marketer for various kinds of products, from e-books to vitamins, Durst says. You need to advertise online at an additional cost and if you don t sell any product, you won t make a penny. Where the rebate part comes in: If you do sell something, you ve got to pay the buyer a rebate, ironically, out of your own sales commission.

Mystery shopping

Mystery shopping is a legitimate niche where organizations pay consumers to shop at specific retailers and then report back on their shopping experience. The scammers version: You are told you will "mystery shop" a Western Union or MoneyGram outlet. You will receive a check with instructions to deposit it in your bank account, withdraw a certain portion of it and wire the money via Western Union or MoneyGram. You are allowed to keep a percentage as your commission. The hitch: That check is fraudulent and your bank will withdraw the money from your account.

eBay PowerSeller training

Yes, a lot of people make legitimate profits on eBay (EBAY) . But be wary of offers to purchase training kits or register for seminars that, often at the cost of thousands of dollars, purport to teach you how to become an eBay power seller yourself. Earlier this month, the California attorney general s office ordered that two such companies pay nearly $350,000 in restitutions to California residents who have or plan to file complaints with the AG s office. The companies promised customers that they could earn full-time incomes by selling merchandise on the Internet, according to Scott Gerber, spokesman for the state attorney general s office. In reality, most people end up losing money and very few make money, he says. EBay didn t return our calls seeking comment.

Assembly and craft work

Crafty job seekers may be enticed by offers to assemble products at home, whether it s gluing together little ornaments, sewing tutu dresses or some other hands-on activity. And such offers could be perfectly legitimate. If so, they will require you to purchase a kit containing the materials to make the product and a sample of that product. But you'll be asked to mail one item that you ve made for the company to approve and only then proceed to make the rest and get paid. Scammers, meanwhile, want you to send them all the items at once and then reject your work with no pay whatsoever.

Medical billing

A classic biz in a box scam, ads for medical billing opportunities tell you there is a severe shortage of people processing medical claims so why not jump in and make some money yourself? You don t need much training to do it other than that provided by the training materials, software and even potential client lists. The catch: Those start-up kits can cost between $2,000 and $8,000, according to the Federal Trade Commission. Once you put out the cash, you realize that finding clients isn t nearly as easy as it sounds, especially for a newcomer to this fiercely competitive business. Most doctors process their claims in house, or use big, already-established firms. It s one of those sectors that s been overridden by scammers, Durst says.