DAX to flag sample based on ID

Really !? 🤔

Now, try this :

Sample Flag =

VAR CurrentID = 'Sales'[Sales ID]

VAR AllSalesIDs =

    DISTINCT( 'Sales'[Sales ID] )

VAR RankedIDs =

    ADDCOLUMNS(

        AllSalesIDs,

        "@Rand", MOD( 'Sales'[Sales ID] * 1140671485 + 128201163, 134456 )

    )

VAR Top3IDs =

    TOPN( 3, RankedIDs, [@Rand], ASC )

VAR IsSelected =

    COUNTROWS(

        FILTER( Top3IDs, 'Sales'[Sales ID] = CurrentID )

    ) > 0

RETURN

    IF( IsSelected, "Sample", "" )

Hope this helps! Don't forget to mark as solution and 👍 in order to keep helping others 🙂