Just ask. Most sales associates, with the rare exception, won't offer you a sample unless you have bought something. I would just ask if you could have one. You could even ask what samples they have. Then you could choose. You might get lucky and walk about with a bunch.
Acqua di Parma is amazing, though. If you want to smell like the ultimate, classy, clean, suave and sophisticated G who might just have a million dollars in his pocket, or he might just have a gun...this is your scent. Old school, soapy, and just about perfect.