Is conversational reframing ethical?

A fair amount of the NLP topics I've been learning about can also be used in a conversational way, rather than in the usual therapist-client manner. Often referred to as 'Covert NLP'. I find this side of things pretty interesting, but I'm still unsure of how I feel ethically about using techniques like this without the other person giving consent beforehand.

If somebody came to see me as a therapist about something, then I'd be fine about using various techniques during conversation, because they've already given their consent indirectly when they came to see me. It's the everyday conversations with people I'm unsure about. The kind of stuff I'm talking about here is mostly just reframing, but in the style described in Mind Lines (which is a great book on conversational reframing).

Is it ok for me to try and influence someone to change a habit, such as giving up smoking? What about less harmful habits such as biting their nails?

Part of feels like it's ok to try and convince someone to change using normal methods (which pretty much comes down to argument), but that it's 'cheating' to use things like conversational reframing for this. But at the same time, I know that trying to get someone to change almost never works by arguing with them, and that what you really need to do is get them to see things in a different way - which is exactly what reframing is all about.