Now, either the salesman lied, or the person misunderstood. I'll go either way. The person also complained about there not being a CBS app. There is a CBS app, so the person will certainly get things wrong, meaning it could have been the salesman said something that the person interpreted that way.
Either way, that's not what Roku does. Nor Fire TV. Nor Apple TV. Nor Google/Android TV.
If you are looking into streaming, be aware that a Roku -- or any streaming device -- does not in and of itself get you live local TV. You get that from an antenna. Or from a subscription to a live streaming service that costs $65/month or more. But just taking a Roku and hooking it up to a TV? That won't get you live local TV.
Now, you can get live TV. There are news feeds. There are streams from other channels that work like cable; you use the remote to launch the app with the channel, then select the channel from those listed inside, and just watch. Roku Channel, Pluto TV, Xumo, and others have content like this. So, while you can find live TV, you won't find live local TV.
You can find apps that carry your local news after it airs. So that is local, but it's not live. It just plays on loop.
And if you want CBS, as our intrepid user wanted, there is Paramount+, which as part of the $10/month plan, gets you live local CBS.
If someone told you that you can add a Roku, or Fire Stick, or other streaming device to your TV and pick up live local channels, you may want to check again. You can't. They either told you something wrong, or you misunderstood.
You can certainly use these streaming devices and get a lot of good content, but just having them won't automatically get you live local TV as part of your Streaming Life.