Messrs Grubb, Grubb and Burrowes
From Tolkien Gateway
Messrs Grubb, Grubb and Burrowes was the company that was selling Bag End and its contents when Bilbo Baggins returned home from his adventures told in The Hobbit. Note the variation in spelling of the last name seen nowhere else. Perhaps this was just an unusual spelling of the name Burrows, though it may conceivably have been an entirely different family of hobbits with a remarkably similar name.