First and foremost - do not EVER pay a company for "training materials" before starting a job. THEY want to hire you for a job, so why would you pay them for training materials? Legitimate businesses will train you at no cost to you, AND they will probably pay you during the training period.

You'll need to trust your instincts as well. Remember how momma used to say "If it seems too good to be true, it probably is"?  Well, this is certainly true when Get rich schemes are just that, schemes. They don't work and more than likely once you've paid for your "training materials", not only will you never see the training materials, you'll also never hear from the company again, nor will you be able to track them down to try to get your money back. Be smart, listen to that little voice inside of your head.

Ask yourself if there website is professional or is it sloppy? Does it look like they went to freewebs.com and put up a site within an hour? If so, be very weary, as it is likely to be a scam.  Not to say that legitimate businesses will NEVER have a sloppy site, but scammers sites will usually have sloppy grammar and misspellings.  Also, if they are using a free web host, like freewebs.com or bravenet.com, this may mean that they either don't intend to be around long enough to purchase their own domain. With how affordable domain names are now, there is no reason for any legitimate business not to have one.

Does the site have contact information for the company on it? Do they have a phone number? If so, call it. Do they answer
as a business or are you getting bumped directly into voicemail?  Do they have their actual location / mailing address or just a contact form? If there is only a contact form, be very careful of this. You could send a million requests to them AFTER they've scammed you and you will quite possibly never hear from them again. I had an experience like this once. I signed up for a WAHM site that I was to have my domain name registered through and my webhosting. Not only did they continue to try to charge me for 7 months after I had tried to cancel the account, they took my domain name that I paid for and I have never heard from them again. 

The application is asking too much information. Does it ask your marital status or how many kids you have? How about bank accounts or your social security number? This is definately a scam. Run in the other direction!!! These questions are illegal as they cannot base their hiring decision on the answers so DO NOT give out this information.  Employers have no right asking these questions and you are not required to answer them!

Visit message boards for dirt on the company you're thinking of applying to. I have found a TON of information on companies I have thought of applying to and its amazing what you may find.  Most people are very candid on the subject of work at home jobs and you could find some invaluable information!

Do your homework.  Take a look at my article 'So you want to make money from home?', it will give you a couple legitimate places to begin looking for work at home jobs.