company websites
A website is the cheapest way to "appear" legitimate. If a company can't even keep a website up, I would be nervous. In addition, I agree with the advice to never email credit card numbers. If you have to pay someone, have them send you a paypal invoice, and pay using that.
If a company has a new product to sell, why not sell it through an exisiting online site (amain, stormer, etc.) This automatically lends credibility to the product. Unless of course, there is no product, or the owners are using purchase money to make the initial product.