If you can find a hashtag that is relevant to your business (such as #SelfieSunday), this is all the better for your business. Due to the fact that these hashtags are already developed, it will allow others who are on Instagram to see the hashtag being used by your follower.
This is then going to garner more attention to a particular product, to new merchandise you are selling or to other relevant information about your product. If it is a popular hashtag and if your followers are participating using images of your merchandise, this is free marketing for you as a business owner, and it is a great way to spread the word about your business and the product line that you offer for sale to your customer base.