. . .claim their customers, wholesalers etc don't know they are self-published?? . . .
Actually, a completely professionally self-published book is indistinguishable in the trade from any other small-press book. No one has any way to know that the author is also the publisher.
I know a good many self-publishers/independent publishers, ranging from rank amateurs (obviously self-published) to polished professionals (nationally and internationally distributed through normal trade channels as well as via the publisher's own website).
One who publishes specialized textbooks (he is an authority on the subject) is sometimes amused to take calls (placing orders) from people who have no idea that his is a one-person business.
There is not a clear line between "self-publishers" and small presses. There are infinite gradations, and it is not unusual for someone to start by publishing one book (might or might not be his or her own) and expand from there. The classic example is Ben Dominitz, who with his wife self-published a book. It was very successful. He added books, eventually developing the highly successful Prima Publishing, which was eventually acquired by a major publisher (Random House, if I recall right).
Badly self-published books are obviously self-published. Professionally self-published books are simply small press books -- the average observer has no clue about who the publisher is.
--Ken
