Best Sales Strategy question

[jillb]

Hello, This is my first post. I'm finalizing a marketing plan for a book my colleague has completed and is self-publishing. His book will be published through CreateSpace. It will be available for purchase through
1) his web site,
2) through createspace directly,
3) on amazon and
4) through distributors like B&N.
Profits decrease with each descending venue, but I'm trying to figure out if it's worth directing sales to amazon in order to boosting visibility and potential future sales.
I'd appreciate any experience/advice in this arena. thanks
JB