One main thing is check for the genuinity and popularity of the site. Just run a google search to find the review on the site if available. There you can get customer reviews which is the main thing to look forward in an online shopping portal.

Another thing is to check whether the site uses encryption. Encryption is very important for a site because you may have come across sites where they ask for Credit card details for shopping. When you give the credit card number, suppose the site does not use any encryption, there are chances that any hacker can steal these information and happily make purchases of his own with your credit card!

SSL encryption is alsso a good method to see whether a site is genuine. It does'nt mean that those without SSL are not genuine. It is like an assurance.

These should help

Most of the E Commerce portal has HTTPS portal, you can see it in the address bar. These are secure channels. It is better to do transactions using these.

For secure online shopping make payment through paypal, or online transfer. Don't give details of your credit card to any website. Use your credit card through paypal without exposing your credit card credentials. This is how I do.