This is very important, so please read the below very carefully:
Please be aware that using someone else's model in your work without referencing them is considered plagiarism.
Also, you won't be credited for that part of your work, so limiting it to supporting models (such as people, vehicles, furniture ... i.e. things to reinforce scale and give context) is advisable. In other words, if a model that was created by someone else is a major part of your design it's unlikely that you will pass, even if it is correctly referenced.
Finally, if you plagiarize and are caught the consequences are very severe. So please, if you are tempted, talk to someone to get help or find another way.
Russell and Andrew