Because visitors are still going to the same destination as the original URL, Google will not penalize you as an advertiser. The publisher can decide to add a "No Follow" tag on his content to prevent you as advertiser to get a PageRank passing backlink or show that these links are placed with commercial interest. We are confident that LinkPizza has if any, a positive influence on your website’s rankings, because the publisher would otherwise have used an affiliate link which doesn’t tell a visitor directly where he is going.