First try to contact the author: http://themeforest.net/item/flatads-classified-adswordpress-theme/7157644/support. If they can’t help, you can contact Envato. If you can show that there theme isn’t working as described and that you contacted the author, they’ll usually give you a refund. Good luck!
This FAQ should help clarify your questions: http://themeforest.net/licenses/faq#item-packs-a. Essentially, each item in the pack has it’s own regular license. So you couldn’t use the same PSD for 2 different clients, you could use each of the 100 for 100 different clients.
Most people just don’t need the extended, especially when it comes to websites. Here’s the detailed FAQ for when you do and don’t: http://themeforest.net/licenses/faq#faq-section-regular-and-extended-licenses.