The only case where a buyer's agent might be paid by the buyer is in a super hot market with a for sale by owner. It has been awhile but some were not paying any commission. Also, I believe you need to have a contract with your agent otherwise they are working for the seller. As a side note - your agent increases his income with a larger selling price. Be sure you trust him to represent you.
Flat rate buyer's agents are not uncommon, especially for high end houses.
The people who can afford $1million houses don't have time to go around and nit pick the color of the back splashes in the kitchen.
Not much difference than using a fixed fee investment advisor, which is the smart thing to do.