While it is possible to scan through a category manually to find duplicate items, it is much easier to use the Lookup Manager Find Duplicates utility.
To perform a search, select the required Category from the Category drop-down pick-list then select the first item in the list to mark where you want the search to start.
Next, select the [Find] toolbar icon from the [Tools] toolbar tab. The Lookup Manager will scan down from the currently selected location in the list and stop when it has successfully highlighted a duplication, or report that no duplicates have been found.
The most basic way of dealing with duplicates is to manually merge them together. Once the list has highlighted a set of duplicates, click the [Merge] toolbar icon to perform the merge process to remove the duplicates and leave only a single copy in its place.
A far more convenient process however, is to turn on one or more of the Duplicate related preferences in the [Options] toolbar tab:
Using these two preferences in conjunction with the [Find] toolbar icon allows very fast processing of even large category listings.