Also, your items have to be small enough to mail cheaply. A piece of furniture, for example, will not sell well if the buyer will have to pay half it's cost for shipping.
I would suggest that your brother make a list of the items he usually finds at estate sales and then do eBay searches on such items. He can then see what sells and what does not.
However, again, you have to be knowledgeable about what you are selling. A friend of mine makes a good bit of money buying old paperback novels for five cents apiece at junk sales and selling some of them on eBay for over $50. When I asked her why anyone would pay $55 for the item she was showing me on her computer screen, she explained that that particular paperback novel was the first novel by a now famous romance writer and that only a small number of copies were printed.
The lesson is that my friend can make money selling paperback novels on eBay because she knows the paperback novel market. However, I would lose my shirt on posting fees since I don't know the first thing about that particular market.
My idea is to see if there are things that are definitely worth buying and things to always stay away from.