I'm unable to react happily when receiving gifts or things like that
What is the basis of your thinking? Why do you feel like that when you get gifts?
There's an event in my past that involves me getting many dirty tricks which made me unable to trust.
Even if you are feeling traumatized about past events you cannot let that control you and not show appreciation for something you got as a gift. It is not their fault and you will hurt their feelings.
So I need to pretend I like everything for their sake. Fuck that.
It is expected that you show appreciation when someone is generous to you. If you want them to stay that way you should be polite.