Some microstocks consider semantical duplicates as a spam. So it might be not favorable to have nouns in singular and plural form as keywords to the same artwork (e.g. having “tooth” and “teeth”).
If duplicates detection is turned on in Settings, Xpiks will highlight duplicates with blue in Keywords field and in Description and Title as well.
In order to fix them Xpiks highlights them clearly for you if you click “Show duplicates”.