Appropriate way to reject an offer
List your good points.

Meaning instead of outright rejecting this person's offer, you say, "I already have such and such already," you get the picture. Emphasize that you are very well off, no need for gifts and such. So if someone offered a gift to you, you could say, "Thank you, but I have a lot of such and such." And the good ol' "I'm on a diet" works well on Chinese too :)