gistfile1.php

// Overwrite meta description for vendor pages
function overwrite_vendor_meta($desc) {

    // Return the default value if we're not on a vendor shop page
    if(!WCV_Vendors::is_vendor_page()) return $desc;

    // Get the vendor description and return it
    $vendor_shop = urldecode( get_query_var( 'vendor_shop' ) );
    $vendor_id   = WCV_Vendors::get_vendor_id( $vendor_shop );
    $desc = get_user_meta( $vendor_id, 'pv_shop_description', true );

    // Remove line breaks
    $desc = str_replace(array("\r", "\n"), " ", strip_tags($desc));
    // Remove extra spaces
    $desc = preg_replace( '/\s+/', ' ', $desc );
    // Escape special characters
    $desc = htmlspecialchars($desc);
    // Shorten it to 156 characters (153 + '...')
    $desc = substr($desc ,0,153).'...';

    return $desc;
}
add_filter( 'wpseo_metadesc', 'overwrite_vendor_meta', 10, 1);