It really goes without saying, if you want to be professional you should probably act professional - most customers will be more comfortable about purchasing from you if you can who you're reputable.
Keep in mind, and you should seek legal advice on this, though in some countries there are regulations that are in place which state you must display certain information about your business on your website.
For e.g. if you're incorporate in the UK, you must display your incorporation details on your website, and similarly in Australia, if you're registered for goods and services tax, you must display you're ABN / Australian Business Number on your website.