Cash back is a great reward and usually offered when you buy a product. Mostly products worth hundreds of dollars may have cash rewards you can claim back say $50 or $100 or more.
Its a point of retail promotion and set your product or product range apart from the rest. It works.
Cashback is a financial tool big business uses to make their products more attractive at the point of sale. It looks like a reward you get at the time of purchase however you need to take to cashback paperwork and fill it out. Then you have to mail it and waitfor the rewards payment. You know what that means that maybe only 2% of people actually claim the cash back rewards. You win if you do the paperwork, how wonderful. The business wins of course with so few claiming the cash back.
Any business could offer cashback. However the business needs to manage the program. The business needs to promote the program.
Online cashback cannot be instant as it becomes a discount. So online cashback will require two steps.