The most common and most likely answer to this crossword clue is the 7 letter word CATCHUP
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The straight part
We know that "What grocer needs to make poor sales equal rival’s?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what grocer needs to make poor sales equal rival’s? = catchup.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CATCHUP mean?
CATCHUP noun- A tomato-vinegar-based sauce, sometimes containing spices, onion or garlic, and (especially in the US) sweeteners.
- Such a sauce more generally (not necessarily based on tomatoes).