Advertise that for today (or this week) this product can be bought by what the customer thinks is the fair price. The product should not have an MSRP printed on it (like a book), and an important part is, that they read (and maybe sign) explanation for why you are doing it. Most important, is including what is involved in pricing a single product in the shop (explaining the cogs, how long they stay on the shelf on average and how much that costs, shipping to the store, cost of money “sitting in it”. Basically, show them the real cost for the store of offering them the product.) Then they can buy it for what they think is fair.
An analysis should follow this experiment to find out if there are interesting patterns of behavior.