A home swap is not a transaction. It is looking after someone else's daily life for a while. The best exchanges we have done felt like the owners had left the house for us to mind rather than simply moved out, and the difference is always in the small things.
Write the manual you wish you had been given. Three pages is plenty. How the boiler works, which window sticks, where the good bread is and what day the vegetable truck comes to the square, the name of the neighbour who waters the plants. List the things that break easily, so nobody feels surprised or blamed.
Leave the house better than you found it. We do a deeper clean on the last morning than we would at home, restock the exact staples we used, and add something local we found along the way. Respect the rhythms, too. If the owners keep a standing Wednesday lunch, do not plan something noisy that day. If they ask you to water the tomatoes, do it like it matters, because to them it does.
We now have a small circle of three families we trade with regularly, one in Alsace, one near Volterra, one in the Bohinj valley. We have never met any of them in person. We know their kitchens and their bookshelves and the view from the bedroom window at different times of year. It is one of the stranger and more sustaining friendships of adult life.