So you sit at the wards all day ready to undercut people who undercut you just so you can get your *** sold? Right, perhaps that's why you don't have a rank 50 yet. You're clearly playing the game right. After all the whole point of FFXIV is to sit by the market wards ready to "compete" with some dude who sits there undercutting whatever price you list your *** as.
The problem isn't so much a random putting one or two items up he didn't want, but the people who can keep that listing restocked. Gathered items are a common one. I apologise for wanting to do more than sit by the wards all day to ensure I can sell my walnut and yew logs. Your gameplay must be very exciting.
If people like you had your way NPCs would be selling every item for 1 gil.