I've worked with several huge publishers in my career. Some of them have contracts, for specific imprints, where they pay royalties on net. Some pay advances, some not. Most of their anthologies cost the authors nothing. To me, net sounds like the author is absorbing at least part of the cost of doing business with these publishers (imprints). I still get their catalogues, and see that many of them are doing POD as well. They just don't advertise the fact to the public. I have worked with many small publishers who pay a percentage of the cover price of the book, tiny advance, and get bookstore exposure. Almost always, with some research, I've discovered that they are either little-known imprints of bigger publishers or are distributed by a large publisher. It's important that authors read every single word on the websites. Look for logos, small print, etc., and if you get a contract, read every word and be prepared to hold your publisher to them. As I am wont to say: "If it aint in the contract, it don't exist!"