Final answer:
The comma error in the sentence is corrected by inserting a comma between "shabby" and "has."
Step-by-step explanation:
The correct edit to fix the comma error in the sentence is to
Insert a comma between "shabby" and "has." This correction separates the adjectives "old" and "shabby" with a comma, which is needed to correctly join two coordinate adjectives. With the comma in place, the sentence reads: The house next door, which is old and shabby, has a "for sale" sign in the front yard.
Learn more about Punctuation in English sentences