This question is not strictly mathematical (as there are not concrete mathematics on it), but I guess that could be of interest to the community.
I am considering to write a research graduate book on some advanced material in my area of research and I am considering to knock the door to a big publisher to see if they would be interested on publishing it.
My question is the following: if interested, which is the usual offer the publisher would propose? I do not know if they pay once (or null), and which is the topic of the royalties (if they apply at some moment of the life of the book).
I have some experience with some non-technical dissemination books not fitting inside one big company (Springer, Cambridge Univ. Press, AMS, etc), and I guess their conditions are way different to a technical book on mathematics.