The only way to stop day-trading is by making player value more transparent for everyone, what a player is worth. Obviously the trade market in bb is not efficient enough, because a lot of people can not say how much one player is worth. if managers would only put players on the market near the fair market price, day-traders would not have a chance. I still believe day traders are necessary to make the market more liquid.
Because the game is so young and the skills and what they translate to on the game engine is open to so much interpretation it is not uncommon for lots of managers to value players differently.
Comparing on as an example to HT you have a mature market with specialist trainers for each position and if you really want to check the valuations of players there are enough experienced users/forums to discuss before making a purchase.
Here we have 10,000 new users in the space of last 2 months and the rest I assume have played the game for coming up to 1.5-2 seasons on average... we have yet to see the impact of player skills enough to properly value their contribution so as this is the case there will be larger discrepancies between perceived values of players.
I know some managers go on visible skills some prefer stats, some a combination.... until certain theories are proved (if they ever can be) then this will continue and you will always have managers speculating on skills that they think will become more valuable.
Love it, hate it, tax it, limit it, it will still happen in some shape or form...