1. Ask Google. I'm sure you must be wondering how possible that is. Its really as simple as it sounds. If you want to find out if a site's offer is a scam, just type the name of the website on google and put 'scam' behind it. Just like this:
2. Check the 'About' or 'Contact Us' page. Most scam sites don't usually have these pages. Those who are smart enough to create one, they do not care to develop it. You can immediately tell from one glance that the site is a scam. You'll notice how poorly developed those pages are. They'll definitely lack adequate information.
3. Who is their Sponsor? Are you applying for a scholarship, a grant or you're entering a contest? Don't be carried away by the mouth watering prizes which may never exist anyway. Make some extra efforts to find out who's sponsoring the website or organization. Especially when such bodies are offering 'gold and silver' for little or no fees. If you can't find out who their sponsor is, you can begin to look out for other loop holes.
4. Check Customer reviews. This is quite important. In fact, it saved me from loosing some bucks some months ago. I wanted to place an order for an apple Mac book which I found very cheap on Amazon. A friend warned me about the seller's offer, so I decided to see the customers' reviews. I was surprised to see that they weren't happy with the seller. He'd shipped a really older version of the Mac book which was totally different from that which he advertised on the site.
It helps. Find out what others are saying about a site or product. I'm sure you'd have made up your mind on what to do before you're done reading the reviews.