By looking at the URL. Usually scammers would make a website with a very similar URL so that the fake one looks very very familiar with the real one. A useful extension for Firefox and Chrome is the Web of Trust extension. It will display a "green circle" next to google search results if the site is voted as trustworthy by people like you. If the site is new or untrustworthy/dangerous, it will display a grey or red circle beside the link. This could be an useful extension as more and more phishing sites start to pop up. The Web of Trust extension is extremely popular and has been around for years. Feel free to look into it.