Slot machines line a back wall and are scattered in other parts of the shop along U.S. 340 beside the Cliffside Inn.
Neidinger said he can sell slot machines in the state, but they are for home use only.
He travels to Atlantic City every month to buy machines that have been retired from use.
One of his favorite places to get used pinball machines in the "deep parts of West Virginia." They are often broken machines, which Neidinger brings back to life in his cramped shop.
Slot machines are priced from $750 to $1,200 and pinball machines have price tags up to $1,950.
"It depends on how pretty they are and how nice they play," Neidinger said.
While the classic pinball machines are favored among collectors, so are they extravagant ones, like "The Getaway," which blares ZZ Top tunes from two speakers on the scoreboard.
"This just came in yesterday, and it's fantastic," he said, pointing to the "Jurassic Park" model.
If the player gets the ball in the right hole, the head of a dinosaur bends over and gobbles the ball and the machine shakes.
Neidinger grew up in Pittsburgh and later joined Navy for six years. He went to Washington in 1952 to work for the Department of the Navy.
For 32 years, Neidinger operated a Rockville, Md., amusement shop considered to be the largest retail store of its kind in the country.
Neidinger had 1,000 machines in his Rockville location but has whittled it down to about 70 in his Harpers Ferry store, which he opened in 1995.
"There's interest, but not to the degree it used to be," he said.