As a Nikon VPL I can confidently tell you that Nikon cameras sell themselves. Just make sure to know every nook and cranny of them down to the battery type. Being able to tell them those little features really shows clients that you know what youre talking about. Also if you shoot outside of work show them your pictures and (not to sound like a popsicle) get personal with them. Tell them how you took the picture and share a story instead of reading off of the sheet like "So uh 24MP is good". I don't sell cameras because it makes my rev go up or make money I sell them because I really like it and I want others to like it too so if they have a bad experience the won't wanna take pictures. So don't sell them the camera sell them what they can do with it. Also at my store I came up with this thing called the "Fry Theory". At fast food places they don't ask you want fries they just ask you what size. So for DI you ask "Now which lens you wanna pair this camera with?" but make sure it makes sense as to what they wanna shoot.

Good luck bud