While you can't technically "buy" a pet from a retail store in the base game, you can if you have the Get to Work expansion.
: You can use a cheat to add a pet to a family you’ve already started. Open the cheat console ( buy sims 4 pets
), type testingcheats true , then cas.fulleditmode . Shift-click your Sim to enter CAS and "Add a Sim" to select a pet. 3. Befriending a Stray While you can't technically "buy" a pet from
: An adoption agent will bring a crate with the chosen cat or dog to your home for an "Evaluation" period. type testingcheats true