aa419 is an organisation that helps in ridding the internet of bad sites that try to steel your money.
Here are some things you can look out for when purchasing online.
1) If it's too good to be true - it most probably is.
2) Do not respond to emails with promises of money, special downloads, virus protection, little pills to make a man more manly etc...

3) Be wise with your money - it you can, pay with your credit card or debit order. This is because banks and cc issuers do have a period where you can reverse the payment if it's fraudulent.
4) Check the site against aa419.org etcetera. or do a google search to see if anyone else has complained about it.
5) Do a whois search, see when the domain was registered - if it's a new site... then it's hasn't been around for long. for co.za domains you can use http://co.za/
for most other sites you can use whois.domaintools.com
6) Remember that around 60-80% of the internet is full or rubbish.. so you should be careful online, and only use sources you trust or who you've been referred to.