How to Switch Decks

Hey there, I've got a pretty common problem. When I perform magic routines for friends and family, I often use a Juggler Ambigram deck. The thing is, when I want to do a trick with a gimmicked deck, like the Invisible Deck or something similar, they always ask why I'm switching out the deck. I tell them it's run out of magic and isn't any good anymore, but they always give me a funny look. Is there anything I can do to keep them from asking, or to give a more convincing answer?

Thanks a lot!