Nursery rhyme vendor (6)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nursery rhyme vendor</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for pieman that I've seen before include "See 1 across" , "Pastry cook of old" , "One Simple Simon met" .)