Calculating a paid price average from user reviews https://www.jreviews.com/blog/calculating-paid-price-average-from-user-reviews

jreviews_overrides|events|listeners|update_listing_average_price.php

<?php
namespace JReviews\Listeners;

defined( 'MVC_FRAMEWORK') or die;

use JReviews\Listeners\Traits\ListenerSetting;
use Clickfwd\Listener\QueueableListener;
use League\Event\EventInterface;
use GuzzleHttp\Client as Guzzle;

\S2App::import('ListenerTrait','listener_setting','jreviews');

class UpdateListingAveragePrice extends QueueableListener
{
    use ListenerSetting;

	protected $queue = false;

    /**
     * Execution delay in seconds when using the Queue Add-on
     * @var int
     */
    protected $queue_delay = 60;

	protected $reviewPriceField = 'jr_pricepaid';

	protected $listingPriceField = 'jr_averagepricepaid';

    public function handle(EventInterface $event)
    {	
		$review = $event->getReview();
		
		// Check if the submitted review includes a price
		$pricePaid = (float) \S2Array::get($review,'Field.pairs.'.$this->reviewPriceField.'.value.0');
		
		if ( $pricePaid && $review['Review']['extension'] == 'com_content' )
		{
			$model = new \S2Model();

            switch($event->getName())
            {
                case 'JReviews\Events\ReviewWasDeleted':

                	// Excludes current review (in process of being deleted) from average
					$averageQuery = sprintf('
						SELECT 
							AVG(%s) 
						FROM #__jreviews_comments AS Review 
						LEFT JOIN  #__jreviews_review_fields AS Field on Review.id = Field.reviewid
						WHERE Review.pid = %d and Review.mode = "com_content" AND Review.published = 1 AND Review.id != %d AND Field.%s > 0
					', $this->reviewPriceField, $review['Review']['listing_id'], $review['Review']['review_id'], $this->reviewPriceField);

                break;

                default:

					$averageQuery = sprintf('
						SELECT 
							AVG(%s) 
						FROM #__jreviews_comments AS Review 
						LEFT JOIN  #__jreviews_review_fields AS Field on Review.id = Field.reviewid
						WHERE Review.pid = %d and Review.mode = "com_content" AND Review.published = 1 AND Field.%s > 0
					', $this->reviewPriceField, $review['Review']['listing_id'],$this->reviewPriceField);

                break;
            }

			$averagePrice = $model->query($averageQuery,'loadResult');

			$query = sprintf('
				UPDATE 
					#__jreviews_content 
				SET %s = %s WHERE contentid = %d
			', $this->listingPriceField, $averagePrice, $review['Review']['listing_id']);

			$model->query($query);
		}		
    }
}

jreviews_overrides|events|providers|custom_listener_provider.php

<?php
defined( 'MVC_FRAMEWORK') or die;

use Clickfwd\Listener\ListenerProvider;

class CustomListenerProvider extends ListenerProvider
{
	protected $listen = [
		'JReviews\Events\ReviewWasFirstPublished' => [
			'JReviews\Listeners\UpdateListingAveragePrice',
		],
		'JReviews\Events\ReviewWasUpdated' => [
			'JReviews\Listeners\UpdateListingAveragePrice',
		],
		'JReviews\Events\ReviewWasDeleted' => [
			'JReviews\Listeners\UpdateListingAveragePrice',
		]
	];
}