...I don't see anything wrong with charging a premium for the convenience of being able to buy an item on the marketboard instead of having to hoof it all the way to the vendor to buy it yourself, nor do I see how this is in any way different from charging a premium for gatherable items. If you don't like the prices the item is listed at, then run to the vendor yourself and pay less. If you're too lazy to do that, and have gil to burn, then I did you a favor by posting the item on the MB so you didn't have to move more than a foot from your usual crafting spot to get it.

That applies just as much, if not more, than if you're too lazy to look the item up or ask your FC if and where it might be purchased. You're unwilling to expend the bare minimum of effort (especially considering that there's no way to play the game that doesn't also offer an internet browser that can be easily be swapped to for a moment), so you pay for that.