As stated, there are gelato shops everywhere. We avoid the shops where certain gelato flavors are bright colors. A good pistachio should never be bright green.
As for granita, prices are not always posted and the price charged sometimes varies whether you’re a local or tourist, even though it shouldn’t. If you buy it from a shop along a tourist street you’ll probably pay more. When we were in Taormina we were charged one price one day and the same shop and seller tried to charge a Euro more for the same thing the next day. We got the lower price.