30% is the industry norm for most marketplaces. I think the App Store & Play store standardized it. I haven't seen anything less than 25%. Comes down to reach -- just checked on themeforest (https://help.author.envato.com/hc/en-us/articles/360000472943-Envato-Author-Fee-Schedule) and they do a similar 55% for non-exclusive and lesser (12.5 - 37% depending on volumes) for exclusive content.