There is an active RETS Forum. Feel free to ask questions at any level; the forum subscribers range from those just getting started to some of those who authored the specification, so no question is too simple or too technical. There are also vendors who can help you with actual coding tasks, providing anything from libraries to full product development.
Additionally, for any questions, comments or concerns related to the RETS website, please direct your questions to help@rets.org. For all compliance related inquiries, please contact Paula O'Brien.