Strangers...

my child is 3 and runs up to any neighbor in the rv park to say hi.how can I explain that not everyone is good...or how to better explain that it's not ok. it scares me, I am the manager and I don't want to make friends here on fear of being taken advantage of, I take rent, enforce the rules, ect... but I don't know how to explain in a way she'll understand...it literally takes me going to grab her hand to get her to come back. please help mom's.