We have an entire page of our corporate website dedicated to RETS/IDX (https://smartmls.com/smartdata/). Not only is this a great resource for IDX vendors interested in setting up a site for an office or agent, but it is a great place for Brokers who are looking to use an IDX vendor to enhance their website with IDX functionality.
Vendors can use this site to access vital information about accessing the SmartMLS RETS server, setting up queries, being compliant with IDX rules and much more.
Brokers who may be in the process of getting IDX up and running on their site can review important information and see questions they may want to ask of potential vendors.
Another good resource for vendors is this document. It was not created by SmartMLS, but it provides good guidelines for setting up queries. Some of the field names will be different for our Matrix system, but this could be very helpful in getting a general idea of how to set things up.