Many of them seem to be from responses to seemingly innocuous enough ads on Craig's List. But there are also ads that show up on the web that advertise, for example, earning $24 per hour doing mystery shopping that may be a source. Just be careful of what you respond to. There are also the "sucker" lists out there of people who have responded to ads for stuffing envelopes or 'processing rebate checks from home' who are also likely to fall for the 'too good to be true' scams.