Plugin pages need demo/test url

Dear wordpress friends,
Is there any posibillity to ad some kind of demo tab on plugin presentation pages?
I wonder why there is no any demo?!
Possibility to see and try how that plugins are working.
Like on themeforest/codecanyon web site.
You can see website with plugin implemented and check out how it works.
Is that becouse plugin developers dont’t have any url with their product installed or they dont have possibility tu publish url where plugin functionality can be tested?
Thank you!