Healthy happy fish with large well cared fore tanks. No dead fish in them not even the feeder tanks.
Drop dead gorgeous, scantily clad females who really know about fish.
My suggestion is to get some system in place for new owners, for example run some tanks with extra media, filters and the like so you can educate new owners about the importance of cycling and be able to speed that process up for them. Provide some leaflets with info detailing the testing required, the kits etc, potential fish stocks for different kinds of tank, and set up some tanks that better reflect how you might have them in your home, not just tanks with all one kind in them
Display tanks! Sales tanks are cool and all, but some really well setup and maintained display tanks can really help get people excited about their tanks.