Since I don't have to write for a living, it's not a matter of life-and-death that I get paid huge fortunes for my novels, short stories and whatnot...
It's a matter of personal integrity and self-respect that I won't get shafted (ripped off, had, scammed, bushwacked, bamboozled, tossed in a ditch and left to die) by publishing people.
If you are trying to get published, you will sooner or later encounter people who
A) avoid paying you money, despite having promised to pay you;
B) ask for up-front "expenses" cash;
C) try to seize all rights to your work.
If you are offered a contract that contains any of the following items, throw it away:
1. The publisher claims all rights, forever. (Read: no time limit or geographical limit is set for the publishing rights.)
2. You, the writer, pledge to perform various services for the publisher, apart from having written the work.
3. Royalties are not offered for sales of your book.
4. You are asked to pay fees of some kind (for example, "editing fees").
5. The publisher/agent/middleman behaves in a dictatorial manner, as if the writer was some kind of serf.
Before I got published for real, I encountered dishonest agents, arrogant assistants, crooked publishers... and I shunned them all.
A helpful resource you must use is the Preditors & Editors index. It lists all known agents and publishers in the Western World, and contains warnings about specific agents/publishers with shady records or a criminal past.