In what sense? If you're thinking along the lines of an on board travel agency, then the answer would be no. If you're thinking in terms of representatives who sold tickets, the answer would be a resounding "Yes." but their activities wouldn't have been limited to booking cabins on the Titanic. The shipping lines typically had a number of offices scattered throughout the UK and the continant and their express purpose was to book passengers on all of their ships.
Some of the agents who sold White Star tickets were in quite small places. Passenger Timothy O'Brien picked up a ticket from an agent in Skibbereen, which even today has a population of only 2,000. I suspect this was typical of Ireland, the home of so many emigrants.