Assuming you have successfully brought the Etsy data into a Numbers table, I think a script is the best way to accomplish something like this:

You don't have to know AppleScript to use the script. You'll know within less than a minute whether it's working for you. (If you have never run AppleScript on your machine you may need to select the checkmark by Numbers.app at System Preferences > Security & Privacy > Privacy > Accessibility.)
- Copy-paste script below into Script Editor (in Applications > Utilities).
- Click once in the table containing the Etsy data.
- Click the triangle 'run' button in Script Editor.
- Click once in an "upper left" cell in an existing destination table.
- Command-v to paste values.
SG
set numColsToExport to 3 -- the number of columns wanted in output
set outLst to {} -- start a new empty list
--put values from table into list of lists
tell application "Numbers" to tell front document's active sheet
tell (first table whose selection range's class is range)
set vv to (rows whose first cell's value is not missing value)'s cells's value
end tell
end tell
-- process the list of lists row by row
repeat with r from 1 to vv's length
set thisRow to vv's item r
set {repeatVals, rowVals} to {{}, {}} -- empty lists to start each row
repeat with i from 1 to vv's first item's length
if i < numColsToExport then
copy thisRow's item i to repeatVals's end
copy thisRow's item i to rowVals's end
else if i = numColsToExport then
copy thisRow's item i to rowVals's end
copy rowVals to outLst's end
else
if r is not 1 and thisRow's item i is not missing value then ¬
copy repeatVals & thisRow's item i to outLst's end
end if
end repeat
end repeat
-- place result on clipboard for pasting into Numbers
set pasteStr to ""
set text item delimiters to tab
repeat with j in outLst's items
set pasteStr to pasteStr & j & return
end repeat
set the clipboard to pasteStr
--return pasteStr -- uncomment this line for testing