Had a massive infestation of Vermetid snails in my 300g FOWLR and found the solution completely by accident.
I introduced a Harlequin Tusk fish and a Niger Trigger and soon the snails started disappearing. Was not sure how this was happening so I conducted an experiment.
I took some liverock out of my sump (infested with the vermetid snails) and placed it in the Main display and the Harlequin Tusk went straight for the snails and started devouring them.
There were some in the hard to reach areas but just made it accessible and he got those as well.
Harlequin tusk is my saviour. My main display is free of snails, but my sump has still has heaps of them, but I guess they can serve their purpose down there as filter feeders.
Might not be the solution for those who have crustaceans and othe snails in their tank as the Harlequin will devour them as well if given the opportunity.