Nothing happens to them, and nothing is charged. An item that does not sell is still yours and still listed until one of two clocks runs out.
The two clocks
An auction that ends without a bid goes stale after 30 days and stops being shown.
A fixed-price listing runs for 30 days and then needs renewing.
Neither deletes anything. Both are a prompt to look at the item again rather than a penalty.
Relisting is free
There is no listing fee, no relisting fee and no monthly charge. You can put the same item up as many times as you like. Does it cost anything to list?
Which means the right response to an unsold item is almost always to run it again — but not unchanged.
What to change before you run it again
The start price, not the reserve. A low start pulls bidders in; the reserve is what protects you. The commonest cause of nothing happening is a start price that looks like a shop price. How to price for auction
The first photograph. It is the whole of your advertisement in a grid of other people's.
The title. Write what somebody would type to find it, not what you would call it.
The time. An item in a show at the wrong hour had no audience, which is not the item's fault.
What the numbers tell you
Your analytics separates two kinds of failure, and they need opposite fixes:
Lots of views, no sales — price or description. People looked and decided no.
No views at all — title, category or timing. Nobody got as far as deciding.
Fixing the second with a price cut is the commonest wasted move. What is sell-through?
Items in a show that never came up
Entirely normal. A lineup you did not get through is unsold stock, not a failure, and it goes in the next show. Nothing is lost. How many items should a show have?
When to stop relisting
After three or four honest attempts at different prices and times, the item is telling you something. Options: bundle it with something that does sell, drop it to a price that clears it, or accept that it is not for this audience. How to list a bundle
Stock that never sells is money sitting in a box, and the box costs you more than the price cut would.
More: can I relist unsold items, what is sell-through, why did my item sell for so little.