I completely agree with everything you posted.
Maybe I've missed a lot of posts in this thread and I apologize if this has been asked before but still:
1) Who decides what is the "fair" value of a player? If it is the current algorithm that shows price estimations - it completely sucks, we all know that. A player who has 18+ in HN/DV and 4 OD is worth very little to someone who plans to train 1v1 for a season or two but then again - he is worth a lot more to someone who plans to train OD... Player value is very much subjective and depends on too many factors. No person or algorithm can decide what it is single-handedly.
2) What happens if I bought a player for 6k and later on sell him for 70k? Well, that's like x12. Will I be punished for making 30k profit, possibly?
3) Is there a difference between making 100-200k profit via listing the player for this particular amount and getting just one bid or listing him for 1 and getting the same price after a bid war? To me - mostly not. What matters is that there was one person willing to pay the end price.
4) How would you determine if the player was trained (improved) during his brief period with the "day-trader"? 'Cause if he was - it is quite natural to want more money or at least a return on investment for him...
5) How would you make the distinction between buying a player cheap and then selling him for fair price and buying the player for fair market value and selling him too expensively? And if you don't plan to make that distinction, how in the world is the first one cheating?
6) Just a practical example: If there are two different stores in town selling the same bread, one for 0.75c and the other for 2.5$ - would the IRS go ahead and tax the second store because I bought my bread from them???