when you go shop and buy stuff, they advertise rm200, you ask them to sell you for RM150 or RM100. Do you offer to pay Rm300?

My sister told me this principle
To get scammed, you need to fulfill 2 criteria.
1. greedy ( people offer you more)
2. stupid

even if you are born stupid, but if you are not greedy, you wont get scammed.
you need a combination of greed and stupidity for scams to work