Clerks and managers say they are also accustomed to an ebb and flow of business.
"Our busiest time is Christmas. Definitely. We get lots for First Communion too. Our business mostly coincides with major religious feasts," O'Malley says.
Not Just Catholics Anymore
Sheehan's Irish past is obvious; from a large selection of old Irish texts to traditional heartshped claddaug rings in the showcases, the store is steeped in Gaelic tradition. But the store's owners broadened their base in the 1960s and now sell to all Christian denominations, not just Catholics.
"The nature of the customers has changed, as has the nature of the trade. We're more ecumenical now," O'Malley says.
"We've enlarged our inventory to accommodate a changing city population," he continues. "There's more Spanish, more Haitians and a bigger evangelical Protestant community."
The titles in the store's book section illustrate that change. Hildegard von Bingen rubs shoulders with feminist interpretations of the Scriptures, and "Preaching for Black Self-Esteem" stands next to Catholic catechisms in a half a dozen languages.
"All kinds frequent the store," says the bearded O'Malley, whose job centers around the book section.
"We get all ages. One interesting trait is people in their seventies and eighties who knew the original store owner, Matthew. They come in and remark on the changes. They knew a smaller store in a simpler time. It's a lot more diverse now--everything is--and they note the change. A lot of them seem put off by it," he says.
But the younger generation is also intrigued by the store's merchandise.
"We get a lot of students. They buy a fair amount, not a lot. Mostly they browse," O'Malley says. "They're curious about the nature of the books. They want to know what these books have to offer."
For salespeople, the store's best-sellers provide an unofficial barometer of Boston's socioreligious status.
"It's interesting to see. The best-seller has been the Catholic catechism. It's the first catechism. It's the first catechism published since the sixteenth century for the universal church," the assistant manager said.
"By contrast, the next best seller came out in 1993. It's The Thunder of Justice. It's part of the apocalyptic end time literature." The book explores the idea that the end of the world is fast approaching and that humanity should behave accordingly, he says. "It's pretty controversial."
For the most part though, Sheehan's customers aren't members of radical sects.
"Most customers are doctrinally middle of the road. There's not so much politicizing...there's a lot of interest in social change though," O'Malley said.
No End In Sight
Although some of the store's authors may prophesy that doomsday is nigh, its management says the store will be around for a while yet.
"We're hoping to be open for another 88 years," O'Malley says."