I thought I would answer a question that I had recently, where I purchased and paid for a product, and then only a week later the product went on sale for lower. Unfortunately, there are no statutory consumer rights if the price decreases, unlike those for manufactures warranty, acceptable quality and fit for purpose. But thankfully, a lot of stores have very favourable return policies.
Many stores allow you to return a product if you simply change your mind, for example Ikea (WA) has a 90 day return policy, Super Amart a 30 day return policy, Big W a 30 day return policy on non-electrical items, Officeworks and Bunnings don’t have any time-limit on their returns. These are only a few examples. Now, generally, if stores offer these return policies, they generally understand that if the price decreases within this period, you should be entitled to a refund in the difference in price.
The reason for this is there is nothing stopping you from buying the product at the discounted price and then returning it on the older receipt with the higher price. The stores would probably prefer this as it means they get a returned product in original packaging.
For my recent transaction, after the store said they could not do anything about the price reduction, only when I explained I wanted to return the item and buy it at the lower price, they got the picture and put through a refund of the price difference.