Dog adoption

So I’m very confused we adopted a dog from an animal shelter and on the website it says there is a fee so they said they wanted to bring the dog by our house to see how he does, well they bring him to our house and he’s good to go and they leave. They said they will be back in a couple days to check on him! Should I expect to have to pay something because nobody said anything about a price ( we were expecting to pay) everyone I have asked isn’t sure since nobody i know has adopted a dog 🐕