For a kid with only small amounts of kid money, it was paradise. I could get a big fat read for fifty cents. And the disorganization was really a plus. A visit to the Apollo meant strange finds and surprises, even if the surprise was a mechanical engineering manual from 1903 wedged in the "Occult" section.
Used bookstores are overstocked with the last few decades' bestsellers in paperback, and the last generation's bestsellers in hardback. You can always see who's dying now by looking through old hardbacks. At the time, it was clear that the generation that read A.J. Cronin's The Keys to the Kingdom and lots of Dreiser had just kicked the bucket. The paperbacks were a mix of 1960s radicals, 1960s radical reactionaries, 1960s freakouts, 1970s aquarium bubbleheadism, 1970s sexytime explosions, and 1970s thrillers. Since those were great decades for sf, I bought a lot of science fiction there too.
This is also where I met Madman Moriarty. He was an employee at the store and was... colorful. More than once he showed up in full 19th century Scots military finery including kilt, tam o'shanter, and assorted belts and medals. Civil war regalia occurred as well. He drifted in and out of a Scots accent. At 13 years old I had no tools for dealing with him, so I just listened as he described his war reenactment club's activities, the glory of Scotland and the Scots fighting man, and many details of military life. He lived to correct small errors in his areas of expertise, but there weren't many people breezing in from the Costa Mesa small business district to talk about Wallace's last battle or the proper method for throwing a World War I German "potato masher" grenade.
Much later in life I realized that the 5149.5 stalker guy who hounded red_maenad at the bookstore and the over-the-top Scotsman who accosted vegemitelover and bruisedhips at the swap meet were the same affable madman who had delighted and terrified me 25 years before.
While I was in Los Angeles the Apollo moved from 18th street to a trailer in the parking lot next to Hi-Time Liquor. Nothing else changed. Over the years I bought some wonderful books there, including old recipe collections, vintage periodicals, and complete editions of both Pepys' diaries and Burton's Arabian Nights.
They're closing now. After 44 years they're packing it in, selling as many books as they can, and putting the rest on the Internet.
If you're local, drop by and say hi and pick up a crappy paperback or two.