Back in my youth, I would haunt the huge book warehouses on Fourth Avenue down in the teens, where you'd be looking at one shelf of books, with two other shelves behind it, for acres up down and sideways. Probably all Starbucks and fashion stores and NYU now.
Self-publishing has evolved into quite something from 25 years ago. Now it is--or can be--entirely legitimate and with better attention to detail than royalty publishers have time to provide. And the secret is that even if you publish with a royalty publisher, you're still doing your own marketing (book tours, etc.), unless you happen to come with a PR agency in tow.
And I'm amazed at the number of people who just want desperately to be "authors." I've worked for two mainline Protestant pastors who said they wanted "author" on their tombstone. Didn't mention thanks to the Big Guy.
I worked for a company out of North Carolina last century, as you say, called Pentland Press, a UK subsidiary. Pure vanity press, with less and less attention to content, although I think they were more legit in the UK.
Right before I moved to the VA/TN state line, I worked on a book that was a woman taking her meager divorce settlement to publish a book containing all the alleged scandals, faults, and shortcomings (physical and psychological) related to her former spouse, in addition to all other violations of theology and geometry (Toole, Dunces) that he may have committed. The book was rank and vile by any measure.
The lady author's name was Goforth, as I came to find out was a not-uncommon name where I moved to, and I shuddered the first time in NE Tennessee, where the author lived, to see a Goforth mailbox.
I thought they'd folded, but a few years later I received another call from Pentland with a more legitimate project. I mentioned my previous experience and told them to go pluck that book of the shelves and scroll through it. They were unfamiliar with the title.
The response I received was one of horror.
From the cited article ...