Paul Cymrot owns Riverby Books on Capitol Hill, a comfortably profitable bookseller that carries on his late father’s legacy. The used bookstore also has a location in Fredericksburg, Va. (Michael Robinson Chavez/The Washington Post)

At first blush, Riverby Books on Capitol Hill is a sleepy neighborhood used bookstore with a simple business: buying books at one price and selling them for a little more, pocketing the difference.

But Riverby is much more. This little enterprise is a lesson in capitalism.

It’s about looking for the hidden gem of a book that will bring thousands of dollars and several times your money. Are you listening, venture capitalists?

It’s about owning your own real estate (they do) so you are not a slave to your lease. Sound familiar, retailers?

It’s about knowing and serving your target audience, who return day in and day out. In this case, the loyal Capitol Hill herd.

It’s about making a low-margin business work.

The result is a comfortably profitable bookseller run by an owner who carries on his late father’s legacy, employs a handful of book lovers who cannot imagine a better job, and makes enough for him and his family to live on.

“It’s a juggling act that requires that I keep a lot of balls in the air, but I love it,” said owner Paul Cymrot, 42. “I didn’t have any idea it would become more than a business and I would still be able to turn the lights on every day. It makes enough money that I don’t fool around trying to think about something else to do.”

Cymrot’s “whistle,” his gift if you will, is carrying on a successful little enterprise that spreads joy — and a bit of cash and good reads — to many whom Riverby brushes against.

Barnes & Noble this ain’t. Riverby’s best year saw $350,000 in revenue and a teensy profit.

It is two bookstores and an online business. There is a “flagship” store in Fredericksburg, Va., that has three times the books of the one in D.C. and returns the profits that make Cymrot’s project go. Fredericksburg is run by Cymrot and one employee. D.C. has one full-timer, manager Lori Grisham, who gave up a job at USA Today to pursue her love of books.

The Capitol Hill store a few blocks from the Supreme Court doubles as the neighborhood’s living room. Pets are welcome: “Dogstoyevsky’s” treats are offered. (Michael Robinson Chavez/The Washington Post)

The Capitol Hill store a few blocks from the Supreme Court doubles as the neighborhood’s living room. Pets are welcome: “Dogstoyevsky’s” treats are offered. There is a fountain and chairs on the patio outside the townhouse, which is owned by Cymrot’s mom, Nicky. Afternoon tea is served every day.

“I know my customers. I know their kids,” said Grisham, 33, whose store is heavy on U.S. history and kids’ books — and light on business books.

The average sale across both stores is a modest $6.35. Cymrot said the stores combined sell about 3,500 books a month; 1,000 in D.C. and the rest in Fredericksburg. Online is about half of overall sales.

Riverby is all used books. The business model is to pay around 25 percent of the price at which the book will sell. Most paperbacks are bought for around a buck and sell for around $5. Hardcovers sell for around $10.

Cymrot endlessly trolls flea markets, estate sales and auction houses such as Weschler’s. Folks consistently walk in with a few, a box or a whole trunk full of books.

“The key is to buy smart and buy good books,” said Cymrot, who credits Grisham with reviving the D.C. store after the death of his father, Steve, who was hit by a car in 2014. “You have to have a passion for books. You can’t fake that.”

The vast majority of the transactions are small. But what makes the business interesting is the occasional home run.

Take the medical book owned by the personal physician to Confederate Gen. Stonewall Jackson. Cymrot estimates he paid $5 for it. The book sold for $1,000.

“If we didn’t do the research, it was just a 150-year-old name in front of a book,” he said.

Cymrot is an avid birdwatcher, a hobby that requires endless patience and a nose for detail — all traits that also lend themselves to finding the long-lost tome that brings in the big bucks.

“It’s not unusual to find that an estate was the attorney general under Truman,” he said, a real example. “You wouldn’t know until you saw his name on some of the books.”

They didn’t recognize one scrawl on a $2 copy of “A River Runs Through It” by Norman Maclean until they figured out the scratch belonged to movie star Robert Redford, who directed the film of the same name. You can buy it for $400.

They are still pondering what to charge for a book with a signature of Judge David Davis, who was Abraham Lincoln’s 1860 campaign manager.

A William Butler Yeats book signed by the poet was bought for $250, sold for $800.

“The Cat in the Hat” inscribed to author Ayn Rand from Dr. Seuss (real name, Theodor Geisel) himself: Cymrot bought it for $25. The book sold for $1,500.

Another homer was the guest book belonging to the head steward on Franklin Delano Roosevelt’s presidential trains. It was signed by Winston Churchill, Will Rogers, dozens of politicians and governors, and others who traveled with the president. Paid $2,000. Sold it for $10,000.

Grisham recently sold several boxes of old Washington-centric yearbooks, church directories, old restaurant menus and high school sports programs to the D.C. Public Library.

“The key is to buy smart and buy good books,” said Paul Cymrot, who credits manager Lori Grisham with reviving the D.C. store after the tragic death of his father, Steve, who was hit by a car in 2014 while walking to buy a newspaper. “You have to have a passion for books. You can’t fake that.” (Michael Robinson Chavez/The Washington Post)

The biggest payday?

The “Simple Cobler of Aggawamm in America,” thought to be the first work of fiction of the United States. Purchased at a yard sale for $2. Sold to a collector for $25,000, a return that would make any venture capitalist giggle with delight.

Cymrot is still working his way through a collection from a rocket scientist named Jesco von Puttkamer, a German engineer who worked at NASA for 50 years.

Puttkamer was an adviser to “Star Trek: The Motion Picture” and creator Gene Roddenberry. He came up with the fake science to make things like “warp drive” sound credible, Cymrot said.

The vast collection includes aerospace books, “Star Trek” script correspondence between Puttkamer and Roddenberry, notes to film stars and photos. He paid $1,000.

Cymrot has a code for buying and selling books that may fetch a price. If someone comes to sell him a book he thinks is valuable, he tells them what he thinks it is worth. A “find” at an auction, flea market or estate sale, however, is fair game.

Cymrot grew up on Capitol Hill, where his folks built a real estate business dating to the ’60s.

Riverby began with an inauspicious yard sale in 1994 when he needed $40 to buy a rare book to complete his thesis on American literature at Brown University.

The yard sale yielded $200-plus, and a used book business was born. He and his dad rented a wall in an antique mall in Fredericksburg, near their farmhouse, and built bookshelves.

Cymrot returned to Brown to finish his education, but his father kept him abreast of the new enterprise, including itemized profit and loss statements, as well as small dividend checks that paid the college rent.

Riverby, named for the home of naturalist John Burroughs, expanded to Capitol Hill in 2001, in the townhouse once occupied by a doctor’s office. Fredericksburg expanded to a three-level store owned by the Cymrot family.

Steve Cymrot was a Harvard-educated attorney who became an established figure on Capitol Hill, bridging the civic, real estate and business worlds.

“The book business was always an activity that Dad and I could do together,” Paul Cymrot said.

After Steve Cymrot died in 2014, the Capitol Hill store remained closed until Grisham — a former part-timer at the Fredericksburg store — asked if she could revive it. “Lori is the only reason the store is open and has stayed open,” Cymrot said.

Cymrot said he has a hidden stash of his prized possessions, such as the guest book signed by the thousands of mourners when the Rev. Martin Luther King Jr.’s body lay in state in the Sisters Chapel at Spelman College for 48 hours after he was killed in 1968.

He said the guest book precipitated what he calls his “Indiana Jones moment,” from the movie franchise about the archaeologist who battles money-hungry bad guys for valuable treasures.

“The Martin Luther King guest book should be in a museum,” he said. “We paid a lot for it by the standards of my little store. It’s a temptation to give it away versus the temptation to sell it.”

The easy money is tempting.

Take his first edition of Jane Austen’s “Persuasion.” “That’s an easy $10,000 or $15,000 sale,” he said. But “it’s in the vault. Not listed for sale anywhere.”

His wife, an Austen fan, will not allow it to be sold unless for tuition — or food. Even some free markets are regulated.