There are web-sites such as these which provide enrichment and other speakers to cruise lines:

http://www.sixthstar.com/about-page/

http://eventzinparadise.com/

In each case, the charges [are/were] $65 per night [Sixth star $US/Events $Aust]. The speaker can take a companion, so effectively the cost is $32.50 per night. I do not know if the whole fee goes to the agent.

The agent will interview and determine suitability [usually at no cost, except for a sample presentation dvd/online etc]. Once the agent finds the speaker suitable, they will facilitate the connection to the cruise ship company, involving presentation of biography and topic list.

It can be a good way to cruise, however once on board, the speaker can be considered a necessary evil by the Activities staff - usually very little contact with the cruise director, but with a designated person.

Scheduling of talks is by the cruise activites team to fit into use of facilities and days at sea. In the role, one sees the behind the scenes mayhem of an entertainment program. Some lines get it together, others fall apart with their logisitics, with the daily bulletin messy with errors, and often conflicts of timing like minded events. My last experience was chaotic and I am considering a change of line for future talks.

Princess Cruises previously handled recruitment inhouse [with a team of speakers in the South Pacific/Australia/New Zealand area], but have now passed it to an agent [maybe different in other locations].

It is certainly an enjoyable past-time, however when sailing as a speaker no loyalty status applies as it does when you sail commercially [in a paying passenger status]. Benefits such as lounge access or "elite" breakfast are not available as the price is so low that the line does not need to offer enticements.