Filter the

gistfile1.txt

<?php

/**
 * Remove the default Sell Media action.
 * We'll replace it with our own custom action hook below.
 */
remove_action( 'sell_media_before_content', 'sell_media_append_media' );

/**
 * Add our new action hook to alter the media (featured image, etc) before the_content in Sell Media
 *
 * @param $post_id
 *
 * @param $content The the_content field of the item object
 * @return string the content with any additional data attached
 */
function my_sell_media_append_media( $post_id ) {
    $sell_media_taxonomies = get_object_taxonomies( 'sell_media_item' );
    if ( is_post_type_archive( 'sell_media_item' ) || is_tax( $sell_media_taxonomies ) || is_search() ) {
        echo 'This message will appear on archives and searches for Sell Media.';
    } elseif ( is_singular( 'sell_media_item' ) ) {
        sell_media_set_post_views( $post_id );
        if ( sell_media_has_multiple_attachments( $post_id ) ) {
            echo 'This message will appear on gallery entries for Sell Media.';
        } else {
            echo 'This message will appear on single for Sell Media.';
        }
    }
}
add_action( 'sell_media_before_content', 'my_sell_media_append_media', 10 );