Hi.
I just engage a solemniser for my wedding in July. I don't think there's a standard requirement or criteria to choose one. For me, I just google for the recommended ones and check out the reviews and see their photos. Selected my top 10 and then just email or call them to check their availability. I was lucky enough to get prompt replies from all of them and managed to get 1 of my Top 10 on my 5th try (I email one first then waited for his/her response before trying another so that i dont get caught in a situation that both JPs are available and i have to reject one).
Hope that helps.
