When Shi Tian realized he had no other choice but to agree to her demand, he still wished to retain some advantage, such as getting paid for the task.
After all, taking the initiative and refusing to see the footage, helped him a bit. Had he really seen the footage before listing his demands, then it most likely wouldn't have been approved.
Why?
Because at that time, it was no longer a cooperation, but somewhat of a blackmail.
Phoebe could easily send that footage to Olivia Harrett and let her know he was the true culprit for her embarrassment. And at that time, things certainly wouldn't look bright.
But thankfully, he didn't, and Phoebe was clever as well. She wasn't going to push her limit since he knew his place and agreed to cooperate.
And sure enough, Phoebe clasped her hands together and smiled brightly.