You can also use FILTERXML if you have Excel 2013 or higher.
=FILTERXML("<data>"&SUBSTITUTE(SUBSTITUTE(SUBSTITUTE(SUBSTITUTE($A$1,"""sellerId"":""","<td>"),""",""mainSellerId"":""","</td><td>"),""",""sellerName"":""","</td><td>"),""",","</td>")&"</data>","/data/td["&(ROW()*3)&"]")
See attached...