Former beekeeper here....swarms are typically very docile. They have nothing to defend (hive) and they're usually full of honey from departing their old crowded home...in search of a new, larger home.
Using a CLEAN spray bottle, spray them down with water if you want to hold them in one place long enough for a beekeeper to get there. When wet, bees huddle tight together and orient themselves so their wings point downward...each bee acting as a "shingle" so the entire cluster is able to shed the water. It's an amazing sight to behold.
Otherwise, they'll move on by themselves like you mentioned.
What are they looking for? Typically, a large living space that is usually guarded by a small entrance such as a hollow tree, loose clapboard siding on a house, and so on.
JB