How do I know internet websites that require credit cards are not a scam?

How do I know internet websites that require credit cards are not a scam?

My mom is a little paranoid and thinks every website will try to steal money from the bank account through a credit card and lose all our money.

So the question is, how can I tell if a website is a scam or not?
And how can I convince her?

Download and Use WOT is a free Internet security addon for your browser. It will keep you safe from online scams, identity theft, spyware, spam, viruses and unreliable shopping sites. WOT warns you before you interact with a risky website. It’s easy and it’s free.

Surf safer and protect your computer.Add WOT to your browser now! Press This Link http://www.mywot.com/

Download and Use McAfee SiteAdvisor software helps take the guesswork out of Web security.

McAfee SiteAdvisor technology is a free download that tests Web sites for spyware, spam, viruses and phishing so you can click with confidence. Press This Link http://www.siteadvisor.com/