How to display custom fields from a plugin

To retrieve a post (or product) custom field, it depends on where you want to display it.

To get a single custom fields:

// in your product loop, 

$reserved_price = get_post_meta($post->ID, '_auction_reserved_price', true);

echo $reserved_price;

if you want to get an array of all your plugin custom fields. You must loop trough all meta for the product

$product_metas = get_post_meta($post->ID);
foreach($product_metas as $key=> $value){
    if(str_pos('_auction', $key) !== false){
        $metas[$key] = $value[0]; 
    }
}

var_dump($metas); // to see the array