What happens if you do not meet the reserve when bidding on an eBay item?

Not all eBay listings have reserves set.

If a listing does have a reserve you will see the Words "reserve not met" near the top of the listing in the official details and they will remain until such time as the reserve is met, at which point they will disappear.

If you don't see that Wording there is no reserve (even though the seller might say that there is in their own description).

When an auction ends and the reserve isn't met, the seller isn't obliged to sell to the highest bidder and can, effectively, withdraw the item. They are able, however, to offer to sell to the highest bidder for the displayed highest bid amount.

The highest bidder is then under no obligation and can accept or decline as they choose.