When I have signings, the store organises books from the publisher. The store pays the publisher and I don't see any of that money. What I do get is a payment of royalties every six months from one publisher and quarterly from the other. One of the publishers gives me 15% of the net sales. So postage of the original freight to get the books to the bookstore, refund and return freight of books not sold after a certain time etc are taken from the gross dollar amount received by the publisher (the price of the book to the store is often 65% of the retail price of the book).
So a book selling for $10-00 at the bookstore brings $6.50 to the publisher who has paid 50c to send it - so I get just under a dollar for the booksale, if I'm lucky.
The other publisher gives me 10% of the store selling price of the book. So that's a dollar for a ten dollar book no matter what other expenses they knock up. In both cases, my contract doesn't allow me to deal direct with bookstores.
If I buy books from the publisher I get a 30% discount on recommended retail price. So my $10-00 book costs me $7-00. I give talks at schools, libraries and groups like National Seniors, Probus, Rotary etc., and sell the book there. My profit, therefore, is 30% less my expenses such as petrol to get to the meeting. In some cases, say evening church groups, they throw in evening meal for free as well! Most bookstores buy me a cup of coffee. They're lovely people, the bookstore staff.
I also send emails (one freeby, thank goodness) to all libraries and schools in the country. I offer to send the book to them postage free, which reduces my profit by about 25% but I get the book out to places of high exposure. I write in the book how the reader can order the book from me, if they want to buy one for a birthday or Xmas present.
So that's my experience. I hope it gives a bit of an idea of my publishers which are Zeus in Australia and Lachesis in Canada. Ask questions if there is any part of the system I've not explained well.