Step1
AVOID work at home websites that mention your assembling products at home for sale. These are companies that supposedly will pay you to manufacture their products. They give you detailed instructions and all materials necessary for assembly. You put the items together, send them off, and collect your money.
The problem is many of these companies find an excuse not to pay you! The most common is that your work is sub-standard or you didn't follow the instructions exactly. So you wasted all your time and effort, and collect zippo!
Step2
NEVER pay for information! Any website that tells you to send a small fee, even $1 for information about a money-making opportunity is a scam. Information should be given to you for free!
Step3
DON'T pay for mailing lists offered by companies you don't know or haven't checked out. Many of these advertise online and in money-making magazines. And the prices are reasonable--$29 for 100 names.
The problem is that many of these companies give you names and addresses that aren't valid! So you'll get a few, very few, that are ok. But the vast majority will be bad. So you wasted your money for the list and the postage!
Now there are legitimate companies that give you real names and addresses that are totally valid. But they charge more. So if the price is too good to believe, then it's probably a scam!
Step4
BEWARE of testimonials that only have initials! If you don't have a partial name, first or last, then it's probably not legit. For example, a rave review from a satisfied customer named C.K. is probably not valid.
Who's C.K.? But a testimonial from Chuck K. may be. At least there's a first name.
Secondly, take testimonials with a grain of salt. Even a full name could be a scammer or bogus. So don't automatically fall for a testimonial. It could be someone in on the act--fellow scammer. Or it could be perfectly legit. You just don't know!
But if you only see initials and no partial name at all, then it's probably phoney.
Step5
CHECK out any opportunity before you spend money! Visit the Better Business Bureau website to see if there are any complaints against that company. Do the same thing with the FTC (Federal Trade Commission). You can also check with the Chamber of Commerce in the city where that business is located. Or in a city where they operate.
These places are often aware of companies that have a history of complaints and are an excellent resource for avoiding getting ripped off. And they're totally reputable and trustworthy, so you don't have to question their assessment.
Authority 
