Working from home as an employee is entirely different than working at a home business. In a home business you have to invest in your product or service. As a work from home employee you are an employee just as if you were going out of your house to work. There are less than a handful of reasons you should pay for a work at home job. Do your research before accepting a job especially if they require any type of fees.
Direct sales companies will most likely require a start-up investment but to me that is considered a home business.
A few companies such as Live Ops will require that you pay for a background check.
You may be required to have certain equipment for your home office such as a fax machine or other office equipment that you don't already have.
Other than that, there are few reasons to pay for anything.
My favorite places to check for work from home opportunities are Indeed.com (search for telecommute, virtual, remote and work from home) and leave location blank. WAHM.com has a great forum with a lot of information geared towards those looking to work from home.
Another of my "tricks" of searching for these types of jobs include doing a search for the business name and including scam after it. This helps bring up various possible scams and complaints with these companies. Keep in mind, most companies make people mad at one point or another so use your common sense to determine whether the information listed here is truly a scam or just someone who is upset with the company.