They do care, and they do ban for selling runs/carries for real money. But he seems to think everyone who sells for real money is unintelligent, spams on the same b.net account they run on, and works out the details in game in various chats leaving an easy to follow trail of breadcrumbs.
You underestimate tracking and datamining. You don't even need anything but a simple "A talked with B", "A grouped with C", "C gave loot to A" type of logs:
1) You can absolutely detect the spambots. They are horribly blatant. The alternative is not to advertise in game, which severely restricts your audience.
2) You can flag anyone who interacts with the spambots by sending them tells/mails/whatever
3) You can track which raid group those flagged characters join
4) Bonus tracking: they haven't joined much raid groups yet / they are undergeared vs the average joiner of pickup raids (more likely to be a carried guy)
5) Bonus interaction: they join a group, and everyone gives them all the loot for which they qualify (more likely to be a carrier group)
6) After the 3rd...4th...5th??? flagged guy who joins the same group of accounts, you have detected your seller group, which you can investigate more thoroughly (if necessary)
You do scoring: each raid joined get a +X% score added based on likelyhood that this is a carry run, and your CM just have to investigate the top scores in descending order. The raid with 60% score won't get investigated. The professional outfit that runs a heroic Uldir thrice a week with alts for a carry gets a 400% score quickly.
You won't catch 100% of the RMT. You'll just catch the largest ones. It's a funnel of interactions: spambots (lots, replaceable, but mostly detectables) -interactwith-> potential buyer (pretty much the only guy who interacts with spambots) -raidwith-> carry group (fewer numbers)