Why is there a need to place a security deposit for some retailers, while others do not require as such?

Some may not required deposit as they are using the SAME SP BILL for billing, hence no additional deposit is required, since there is existing one in SP side. However, there are also some that completely dont require deposit, likely to get hold of market share first as a tactic, but if u check out their tnc's, some say they might charge it in the future.