I’ve actually had a lot of experience with these kinds of people. It’s really sad that the majority of these prosperity teachers seem to come out of my tradition

. Anyway, a lot of it is just scripture verses taken out of context. Know your Bible; these people are really good at telling a good story, for example Jeremiah 29:11,
For I know the plans I have for you, declares the LORD, plans for welfare and not for evil, to give you a future and a hope.
This verse will usually be quoted alone and in the context that God has a great plan and destiny for your life. Only problem is that the verses immediately before this one tell how the people of God were being sent into Babylonian exile for seventy years.
Another is the story of the starving woman and the prophet Elijah who asked for her last food in 1 Kings 17. This story is often used to say that even if a “man of God” asks you for the last thing you possessed you should give it to him and expect that God will bless you.
So know your Bible.
This theology is based on the (wrong) belief that Jesus came to earth poor and suffered so that we might be rich and blessed. The easiest way to combat this belief is to tell someone who is caught up in this false doctrine about the way that the Apostles and early martyrs suffered and died. If Jesus and they suffered in this life, we should not expect anything less.
It is also based on the “Law of sowing and reaping.” Traditionally, this was understood as sowing and reaping in terms of the harvest of souls. If you use what you have to evangelize and minister the Gospel to people, Jesus would trust you with more resources to reach more people. Somehow, it morphed into what is called “The Law of Sowing and Reaping.” If you give money, clothes, cars, watches, houses, etc (in other words “SEED”) and plant that seed in good ground (i.e. the ministry of whoever is speaking) then you will get a good harvest.
This is based on a lot of scriptures that do touch on sowing and reaping. However, these scriptures are narrowly defined usually to such things as money and other types of wealth. It is important to show someone caught up in this that these passages are being interpreted narrowly.