the shop that bought from me is shut Tuesday and Wednesdays
I think you're saying that the buyer owned a shop, or at least worked in one, and gave this shop as address for delivery? (i.e. that this was not a click and collect delivery to an Argos store or similar.)
What counts is whether this was the address that eBay gave you as the delivery address. If so, according to their money back guarantee policy you will not be required to refund them if the tracking record confirms that delivery was attempted.
However, if the buyer simply asked you to send it to the shop address, and not the address provided by eBay, you will just have to keep your fingers crossed. Unless you have proof of delivery or attempted delivery to the address provided by eBay, you will automatically be required to refund the buyer if they open a case claiming not to have received it. It would be irrelevant whether it was delivered to any other address, even one they provided.