I'm trying to book S7 flights while avoiding booking class W - it does not earn miles for me. S7 website doesn't show the booking class it's going to book and neither does the cheapest OTAs. Any advice how to find out when the flights are going to be booked to something else than W? All tips and ideas are welcome. Even sketchy Russian OTAs!

Well, I`ve found there's an easy and a complex way to to this. The easy way would be selecting "economy Flex" on the S7 site - that always booked me into mile-earning fare buckets. Although I have to admit that my data sample size is rather small, as I`ve only done this two times.
The complex way would be using first using ITA matrix to find the cheapest available fare with a mile-earning booking code: Just put c:s7+ /f bc=O|bc=q|bc=N|bc=S (those four are the cheapest buckets earning miles on AAdvantage) into the 'outbound routing codes' and 'return routing codes' box, select the flights you want and then go to bookwithmatrix.com and paste the matrix results page in there. With some luck, there'll be a click-through to an OTA you can purchase your flights on.
If there's no luck, well, visit a brick-and-mortar travel agent with the printout from matrix...

Thanks. While booking from agent.ru OTA it shows the booking classes and "economy flex". It will still book into W regardless. Some airlines haven't tied their flex tickets to higher booking classes but just add fixed price premium to the cheaper class. Not confident booking 16 legs (although very cheap!) with just this guess!