This is from TOEIC (test of English as international communication) test.
I know the correct answer is 3, which is shown by the examiner.
In this context, however, I think 4 can also make sense.
"When a customer has a happy and smiley face, I'm satisfied with it. It's a proof that my service toward them is going well, which makes me satisfied too."
Is it possible for native speakers to think in that way?
No, TOEIC is right that the only correct answer is #3 - "satisfied." The concept of a "satisfying customer" is a bit odd, though not impossible, but the link between the two concepts of a "satisfying customer" and a "happy customer" is just too tenuous to work in this sentence.