@Cosmin28 I'll try to make it less confusing for you.
The Pay Less Upfront option has nothing to do with the cancellation policy which is in place for a listing. It is simply a convenience for guests so they don't have to come up with the entire amount when they book.
Any cancellation refund due is based on the nightly rate which was charged for the reservation, and isn't dependent on whether you paid the whole shot up front or only half.
So to use nice round numbers, if your reservation was $100 and according the cancellation policy, you are due back 50%, you would be due a $50 refund. If you paid for the entire reservation up front, you would receive $50. If you only paid half upfront, you won't receive anything back because the $50 you paid was only half of the total amount due for the booking.
Your friend Joe books Happy Home by the Lake. Joe has no problem with cash flow, so he pays the entire $100 reservation at the time of booking. Joe needs to cancel within the 50% refund window. Joe gets $50 back. He is out-of-pocket $50.
You have some car repairs this week, so you can only afford to pay half up front to book Happy Home. You decide you need to cancel within the window for the 50% refund. You get nothing back because you only paid $50 to start with. You are out-of-pocket $50, just like Joe.
Read the cancellation policy for a place you want to book very thoroughly. There are rules about whether any refund will be due depending on how far in advance you made the booking and how far in advance you cancel.