With the Custom Thank You Pages extension you can do exactly what it says; configure custom thank you pages, per product. The thank you page is a very powerful place that can be optimized, which not many eCommerce sites do. Why is it such a powerful place? Customers have just purchased something, giving you their hard earned money and more importantly, their trust.
Assuming you sell something amazing, the customer will have a good feeling about their purchase and probably a boost of endorphin (having a feeling of euphoria). As you can imagine this is the best time to use that feeling and interest for good.