I'd be pretty mad too if someone asked if any of my pets were for sale. It would go something like this... (imagining i was with Zsa-Zsa)

Person: Is that cat a british blue?
Me: Yeah. She's beautiful isn't she?
Person: Is she for sale?
Me (look inquiringly at person as if they have brain damage) err...no, she's mine
Person: I'd buy her from you.
Me: Would you now? Well TOUGH LUCK!!!! (storm off)

LOL, but that really would happen