I have tried to give a new created user access to Smart Slider3. The new user sees the smart slider, but cannot change any available sliders nor create a new one. I found a video on how to give the user access to smart slider here: https://www.youtube.com/watch?v=2Nnihte55K4
I followed all the steps, but I cannot find the wpas_user box I need to un-tick.
SmartSlider added these custom user capabilities:
smartslider
smartslider_config
smartslider_delete
smartslider_edit
So I think you need to grant to your user at least: smartslider, smartslider_edit, smartslider_delete user capabilities to give him access for editing sliders.