After our Search Engine Optimization service, web site organic visitors increased by %70. 

Generally, quality of traffic drops slightly when a significant increase in quantity of traffic happens. This is due to assumption that most targeted visitors are already visiting the web site. If you reach more people, they are less likely to be better engaged at your site than your core audience.

What is interesting is that, in our case, all other KPIs also increased. Meaning that all KPIs including bounce rate,  pageviews, average session duration also improved significantly as well as quantity of organic search traffic.