I’m a little bit confuse with ‘Exclusive Author’, what if I sell my rejected item to different marketplace. Will it affect my exclusivity with other items?
no, the only thing exclusive means is you cannot sell the exact SAME item elsewhere.
So if you have a WordPress theme for sale here, you can sell the PSD/HTML elsewhere if you want
You can sell whichever item you wish on any other market AS LONG AS IT IS NOT in your ThemeForest portfolio. Your ThemeForest reviewed and approved items fall under the exclusivity terms and only them.
You can of course sell cross-platform (PSD, HTML, WP, Drupal, Joomla) variations of them. You can sell the HTML, WP here and the PSD on your site or another market.