We haven't asked about the payments, since our wedding will likely be really small, and we just started planning, but that would be very good to know.
We are using a local travel agent. She has experience in destination weddings, and is really, really good. She has answered every question/email (we were out of town for a while) within hours (at the very most), and so far we are quite happy. At first I was hesitant about getting someone who wasn't a specialist in destination weddings, but after talking to her I was totally put at ease. Hopefully it continues on this well!