Here's a simple answer to this question. If any company asks you for money to hire you, then it is likely a scam. No legitimate employer asks employees to pay to work for them, and that includes telecommute friendly companies. Never pay to work.
It's sad, but true - there are plenty of people out there who can't wait to part you from your money and give you nothing in return. Remember, a legitimate company will never ask you for money. Some of the most common scams include Envelope Stuffing, processing orders from Home, home typists with no experience, craft and product assembly, and email processors. The best clue to whether or not an ad is a scam is if it asks you for any money to work for them. Never pay for a job and you will always stay scam-free!