Authors are usually shocked when they discover how little of the cover price of their printed book they get to keep. This is the opposite of eBooks where they get to keep most of the sales price.
Thailand is no exception to this and the lack of competition in the English language book retailing in Thailand doesn’t help at all. Expect the retailer to demand a 50% discount, possibly a consignment deal where they do not pay until they sell the book, and expect them to return books they don’t sell and sometimes in not very good condition. Distributor will of course need their commission. Once you start doing the arithmetic you can see that unless a book sells very well it’s quite hard to make money this way.
Having said the above it must also be said that some authors do very well here. A best-seller can run and run. One just has to think of Private Dancer by Stephen Leather or Only 13 by Derek Kent to see success stories.