Warning: Do not use ONCA Travel Agency in Flores. Rip off!
Do not book with them! You do not get what you pay for.
We booked a transfer from Flores to Panajachel (overnight bus). The guy in the store is called Ronald Lopez (other guys there are named Cesar and Jimmy). The store is located on Isla de Flores in the inner road (not the one at the water, but one road more inside) behind the green monkey hostel.
They showed us pictures of the three bus options: Second class, first class, and luxury. We paid 350 Quetzales for the first class bus. When we got picked up and brought to the bus station, there was only the second class bus and we had no other choice than taking it. The first class is supposed to be long leg space leather seats and comfortable travel buses. And those buses exist, since I had friends who took those buses. This bus was just an old run down bus with barely leg space. So he just booked us in the second class bus but got the money for the first class one (which was 100 Quetzales more).
We arrived at 5 am in Guatemala City and should be picked up at 6 am. At 8 am we called Ronaldo the first time and he said in 45 minutes we will be picked up. After 1.5 hours we called again, he said 10 minutes… After that he did not answer the phone anymore and did not reply to texts even though he read them. 5 hours later a taxi came and picked us up and brought us to another bus station where we were put into a chicken bus to Panajachel. After 16 hours we finally arrived at our destination.
Not only that he screwed us over, he also let us wait for hours without knowing anything. Please try to avoid this lying sneaky guy!