Some owners will certainly carry these 9mm guns in belt holsters. Of course, with that type of carry, you might want to steer them into something with a bigger grip that has better shooting characteristics and holds a larger magazine: the Glock 26, the Smith & Wesson M&P Compact, and the Springfield XD and XD(M) Subcompacts all come to mind. In large part, though, slim-nine pistols are going to be carried in pockets, mostly trouser pockets, and the guns I've just mentioned are a little thick for that application.
Make sure the customer has a dedicated pocket holster for this pistol, and knows the importance of having nothing else in that pocket but the gun in the pocket holster. Loose keys, a small lighter and other kinds of pocket paraphernalia can find their way into the triggerguard and, in the course of ordinary movements, exert rearward pressure on the trigger.
Most of your customers already know this. Some of them are concerned about the trigger getting fouled in a keychain hanging from their belt, perhaps causing an accidental discharge. It's a concern that you, the dealer, can address easily. One option is to sell them a pistol with a manual safety, such as Kimber's Solo or the Ruger LC9. The thumb safety on the LC9 is set up for right-hand use, while the one on the Solo is ambidextrous.
Another option is a hammer-fired slim nine. Because the hammer has to rise on these double-action-only pistols before it can fall and fire the gun, unintended discharge upon holstering can be prevented by the user simply pressing his or her thumb firmly against the hammer as they slowly holster the pistol. This will allow them to feel the hammer if it starts to move, and prevent it from doing so. Hammer-fired slim nines that allow this procedure include the...