I can tell how it is in Liseberg. Usually you start queue, and then when you have queued for a while, you show your pass/ticket to a worker, it is quite close to the ride itself. And then you are let into a second queue/schaffolding part, usually the sorting area for the coasters or the "cut off area" for the maximum number of riders for the flat rides.
There's never a person standing at the very beginning of the queue. There are usually queue time sign there though, along with the ride name. And then there's door/gate that can be put to stop people from entering the queue when ride is down.
There's never a person standing at the very beginning of the queue. There are usually queue time sign there though, along with the ride name. And then there's door/gate that can be put to stop people from entering the queue when ride is down.