第一处是never前加have,这是必须的;第二处我把before去掉了,因为你用现在时don't know不存在before,要是用它的话最好用现在完成时;第三处把定语从句用非限制性的,且替换掉原来重复的the people
The people,who have never been here or those have a purpose to do an adoption,may want to find out something that they don’t know or change their own imagination about the animal shelter.