We booked with HAPPYtoVISIT.com and it was very simple. We paid in cash at the meeting point. As everyone had arrived early, we were able to leave 15 minutes ahead of schedule, and given that it was Easter Sunday, there was literally NO ONE at the border crossing.
As for the tour itself- it's a great value, especially for the money. We had plenty of time to visit the 3 different places, especially Mostar. However, I would have liked more information about our various destinations. I think our guide was attempting to, but there was something wrong with the microphone in the mini bus. The mini bus itself was pretty comfortable; I enjoyed being with smaller tour group vs being with a massive crowd. Also, although he spoke semi-fluent English, he spoke very quickly without natural breaks in speech. It was often times difficult to understand him, so be aware if you are hard of hearing. That being said, he was very nice and surprised us all with burek, a traditional pasty.
Our guide in Mostar (Sasha) was fantastic, but the tour is very short. This is great if you want a lot of free time to roam around the city, but I definitely could have used more time just learning about the city from a local.
Overall, this tour is worth the money. There are things that could have made it better, but we had a great day and got to cross another country off our list! If you're in Split for a few days or more, I recommend joining this tour.
Daily Tour to Mostar, Počitelj and Kravice Waterfalls from Split & Trogir