I didn't find any post/topics on this yet (or did I miss them?), but I just wanted to put out there that tourist visas can be refused as well - ours was (2 people, German and Italian passport). We booked a 5 day tour with Owadan the 7th of March, and they told us that the application was rejected the 19th of March. We then applied for a transit visa in Tehran, which ironically we got - we only decided to go for the tourist visa in the first place because it seemed safer, but apparently there are rejections too. I guess they are fewer than those for transit visas, maybe someone else has similar experiences? Or are we the only ones who had a tourist visa rejected?
