You can decide if the single order amount under a certain limit must be marked as a potential fraud check. To do it, you must enable the option Enable order amount check (for orders not reaching the below specified amount).
For example, if you have a shop with expensive products and the minimum order amount that a “normal customer” usually places is about $2000,-.
Based on that, you decide to set the threshold to $1000,- (through the option Minimum Amount).
If a customer visits your shop and places an order of $800,- it will be marked as suspicious.