In the dictionary, I found this example (Source):
I would appreciate it if you paid in cash.
Clearly, this is the conditional sentence, type 2 which expresses something that is impossible in the future or at the present. For example the following sentence expresses something that is impossible in the future or at the present:
If I won lottery, I would buy a 10 bedroom house.
So, let’s say you want to buy a newspaper at a shop; you give your debit card to the seller; and the seller says:
I would appreciate it if you paid in cash.
Does the seller think that the chance that I can pay in cash is impossible?
Why can‘t the seller use the following conditional sentence, type 1, meaning something that is possible in the future or at the present?
I will appreciate it if you pay in cash.
This way he says that he thinks that the chance that I can pay in cash is possible.
So, which structures do native people use?
I would appreciate it if you paid in cash.
I will appreciate it if you pay in cash.
would
instead ofwill
. seems like a way simpler explanation than stoneyb's answer.