I wanted to know how is the use of models uploaded by third parties. In the case that they use it for their own gain what measures are taken?
Who would take these measures? Litigation is expensive.
Models on this site are supposed to be have credit given back to the original creator, but that is not really something which can be enforced.
When people try to re-upload models and take credit for them, the models can be reported, and the staff will remove the model, and sometimes the account.
If someone has taken one of your models and used it for their own gain, there is very little which can be done.
I'll agree that they should not use the model that way, but it was uploaded to a public site.
Your best option may be to contact the third party and ask them to stop. After that, you could post several complaints about the third party on various websites. There are many cases of intellectual property being taken by others without credit given, sometimes this leads to an extensive boycott, and/or a letter writing campaign.