If someone never acknowledges receiving presents, or thanks you for them?

[Jenni]

If they don't thank you or even acknowledge the receipt of a gift, you should come right out and ask them. Ask them something like, "Oh, you didn't mention if you got my gift. Did you get it? Did you like it?" After they answer, just mention that you weren't sure if they even received it since you hadn't heard anything about it.

This should give them a clue that they need to acknowledge the receipt of the gift. If it continues, you should assume that they don't appreciate your gifts and you just shouldn't waste any more of your time, energy or money in getting them for them.