Posting to Reddit on to promote your business should be done carefully. Redditors are quick to sniff out issues with content and are ultimately the gatekeepers of what gets the most exposure. From my experience, posts from businesses that are honest and provide quality content will do well. When writing a post you need to make it clear that the post is on behalf of your business and not from an untrue source like a customer. Posing as a happy customer can seriously do you more harm than good. Reddit never forgets. Redditors will often take the time to check your authenticity, often looking through your account to check your credibility. Its better to post from your regular account than to make a new account for your business.
Like most people Redditors do not like to be marketed to, there is even a subreddit called /r/hailcorporate to expose suspicious content. To compensate for your marketing you need provide quality content that will intrigue its readers. What distinguishes good content depends on the subreddit, for example if you post on /r/entrepreneur about experiences starting a business it would most likely do well. Depending on what your selling you may have something to offer to niche subreddits. Your story is an important factor to have in a post, it makes your content much more interesting.