The best way for you to communicate with a seller on the app is to do so via the video calling option.
If you're a buyer on Camlist, this will allow you to view the pet you're interested in, and speak with the seller over video. It's the next best thing to being there in-person! You can use this as an option to ask the seller to see the parents of the pet, or have a look at the environment in which the pet has been raised.
On your chat window for a listing, you can see the video calling icon on the top. Once you've tapped it, it will invite the seller to join in. Once they join in, you should be able to speak to them and see them. In case they do not join, they would have missed the call but, they would still have received a notification of your attempt to call them.
In case they make the call from their end, you will get a notification on the app to join the video call.