We've all seen the ads: Make big bucks at home stuffing envelopes! The government says the people behind such ads are scam artists. Over the past 14 months, the government says, it's been cracking down on 200 such operations that have bilked thousands of people out of more than 100 million dollars. In a typical scam, authorities say 30-thousand people signed with Pennsylvania-based National Home Assemblers to make refrigerator magnets. Each paid 50 dollars for starter kits and other fees. In most cases, their work was later rejected for "quality reasons." Other companies have offered bogus opportunities doing medical billing, designing Web sites or selling surplus merchandise. Some scammers have received jail terms, others fines. But hundreds of companies remain in business.