The best way to decide whether to trust an unfamiliar person or website is to consider incentives.

Given the particulars of a given proposition, would the person (or website operator) profit more by delivering on his promises, or by absconding with your money as a "fly by night" operator? Has he expended a large amount of time, effort, and money on maintaining an office, acquiring equipment, and developing technology to be able to fulfil his side of the proposition? Would his reputation suffer if his policy was dishonorable, and does he have an incentive to care? What remedies would be available to you if he fails to deliver?