Not all resources in the Internet provide poster template free. Some of them give away the template for free with limitation, some with proper credit whether for use online or offline, and some can be used for free without any limitation. For the models can be used with limitation, the designer of the template want you to try first of their creation. Once you like it you can buy. Some of models given away with condition like attribution. This is you have to aware that creating poster template is not easy and the author only want you to respect them. The last models are free without limitation. This kind of poster template is sometime attributed with Creative Common 0 or Creative Common Zero, which is already putted into public domain.
Through this website, you can use poster template for free without any limitation. Because all of the templates are believed in the public domain and they are free to use for any purpose without need of attribution.