If a bridegroom should ask you if his bride is pretty, you may lie, no matter how bad she looks. To tell the truth would diminish his joy, and in this case, you should lie. I suppose the same is true if your wife should ask you if she looks fat.
The same is true with any nonrefunduable acquisition. You should rave about the wonderful house your cousin just bought, no matter whether it was a good purchase on his part.