We have joined three Home Exchange sites as well as the Affordable Travel Club. Each site charges a nominal fee, ranging from $60 to $100, for an annual listing. On the listing, you provide all the information which would be useful to potential visitors: pictures of your home, preferred dates, destinations etc. Once you have registered with an agency, you will be provided with weekly emails which will inform you of new and updated listings of other members who have indicated their preferred destinations which coincide with yours.
The listing agency does not do any vetting of the integrity of the individual listing. It is up to the individuals to develop that sense of trust. The underlying assumption of course is that you will take care of the home of the other people as they will of yours. Arrangements regarding an exchange of cars, care of pets, accommodation of children, etc. are all negotiated by the people interested in the exchange. Our experience has been in the positive without qualification. One tends to get people who are professional and like-minded. To this day, lasting friendships have developed because of our home exchange experience.
In the case of the Affordable Travel Club, no exchange is involved or any responsibility to reciprocate.
Both, the Affordable Travel Club and Home Exchange Agencies list people who are interested in house sitting or pet-sitting. We spend six wonderful weeks in the Basque Country of France, looking after four cats, when no reciprocal arrangements were negotiated.