Niches like this abound - such as programming tools, clipart, fonts, home and hobby, religious software, etc. Do your own reviews and ratings. It's expensive and time consuming but there's no better way to make loyal customers than to present them with the best tool for the job. Keep them from needing to spend the time to look at a number of packages and they'll look to you for software first. Tell your customers how to use the software.
Customer service is always important.
Give customers an easy way to get in contact with you. Let them ask questions and give them prompt answers. You'll get lots of people asking what program they should use - if you investigate and direct them you'll have a loyal customer. Even if you don't review or rate software you can still spotlight exceptional programs that your customers will like. To do this, you need to know your customers and know their buying patterns.