The end of a wifi session is always so awkward for me. What do you guys think is the best way to do it? If you're trading, should you end the multiplayer session or should they leave via the train?
I usually escort them to the train station since I don't mind. I've flipped the switch because we'd agreed to that or because they asked.
Whenever I've visited other people's towns, I've gotten a bit of everything. I've met people who have flipped the switch without warning once the trade was finished, while others just took me to the station or announced it in advance. I've never felt like they were being rude, since I usually keep in touch with the people I'm trading with through PMs.
If you feel rude flipping the switch, you can let them know in advance that you're going to do it (when you start talking through posts or PMs), ask them, or not do it at all. Asking people in-game is probably not very effective, because if they don't know what you mean, it might be more awkward and complicated to explain.
- - - Post Merge - - -
I have to note that when I'm a visitor, I just try to figure out what I'm supposed to do or I'll just ask. Once a trade is finished or once I've talked to a villager, I'll thank my host. That's when they can say something, start walking, or flip the switch. If that didn't work, I'd just say goodbye and start walking to the station very slowly to give them a chance to catch up or end the session themselves.