There are many variations on this cobbler proverb, but here is the oldest I can find, reported to be from John Heywood's Proverbs part i chapter xi, published in 1546 (and quoted later by Richard Graves in The Spiritual Quixote, published in 1773):
But who is wurs shod, than the shoemakers wyfe, With shops full of newe shapen shoes all hir lyfe?
A couple of similar quotes are:
A plumber's house always has a dripping tap.
A blacksmith's home only has wooden spoons.