The fact that anyone can buy agony infusions on trading post makes lower tier fractals pointless. Consequently players with no fractal experience can start directly to do tier 4 fractals. It adds up some frustration in tier 4 fractals for them and their teammates.
I suggest making agony infusions account bound so it is not possible to buy those in the trading post which will force new fractaleers to start learning fractals when they are supposed to start. On the counterpart vetaran players who no longer need agony resistane will suffer of not being able to sell those. To compensate a good solution would be to make the base price of agony infusons a little higher so it is profitable to sell them to NPCs. What do you think ?