Identifying rows with similar criteria

Dan- The formula is easy. What do want to do with the result? A sample workbook / mocked-up version showimg what you're after would be helpful. For example, I could Highlight any qualified products within the main list, or build a separate list.

Try

C2

Formula:

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c2=IF(COUNTIF($A$2:$A$9,$A2)<>COUNTIFS($A$2:$A$9,$A2,$B$2:$B$9,$B2),"duplicate product with different size","")
Try this and copy towards down

For highlighting

select A2:C9 and then press Alt->O->D ->>New rule->>use a formula to determine which cells to format->>> use this =COUNTIFS($A:$A,$A2,$B:$B,$B2)=1 formula in formula section the select the format as you want then ok.

or
=IFERROR(INDEX(C$1:C1,MATCH(A2,A$1:A1,0)),IF(COUNTIF($A$2:$A$9,$A2)<>COUNTIFS($A$2:$A$9,$A2,$B$2:$B$9,$B2),"duplicate product with different size",""))
try this and copy towards down

OK, Dan, here's your workbook with a list of "Dual-Sized Products" in Column E. I defined the following 2 dynamic Named Ranges:
(These adjust to changes in List size.)

Product =OFFSET(Sheet1!$A$1,1,0,COUNTA(Sheet1!$A:$A)-1)
Size =OFFSET(Sheet1!$B$1,1,0,COUNTA(Sheet1!$B:$B)-1)

...and here's the ARRAY FORMULA that creates the list:
=IFERROR(INDEX(Product,MATCH(0,COUNTIF($E$1:$E2,Product)+(COUNTIFS(Product,Product,Size,"Small")*COUNTIFS(Product,Product,Size,"Medium")=0),0),1),"")

NOTE: When pasting an ARRAY FORMULA in the formula bar, you must press CTRL+SHIFT+ENTER to confirm entry.
Then use the drag handle to copy it down as far as needed.


DUALSZ.png

Hope this fits the bill.-Lee

Please click the Add Reputation star below any helpful posts, and if you have your answer, mark your thread as SOLVED (Thread Tools up top). Thanks!-Lee