Most customers like to pay around 104% of the base price for Near/Just Pin. There are some exceptions, like the Old Man whose sweet spot is around 108%, a couple others are around 105-106%. Red items have the greatest variation here, so either ask for around 230-250% if you don't care, check the Wikia page for "exact" percents (these are a bit iffy but work sometimes).
For red items, I just double my normal quote, for blue I halve what I'm willing to pay. I think this is conservative actually, I suspect that the multiplier is 2.1 or something similar.
Also note that some customers are bipolar. I'm especially thinking of Louie, who will sometimes "really want this" but he's "broke this week." If the item is something that will boost his adventuring stats, sell at 80% or even less.
The same for getting top-end gear into the hands of a new adventurer. I remember selling a Hurricane Bow to Elf Girl (Tielle?) for less than 1000 pix. I did not regret it one bit.
It's possible that rep affects the amount, so if they don't know you that well, ask for a bit less than 104%.
Reputation does affect the prices, but 104% is a good starting point. Once they really like you, most customer types will Near Pin at 108% fairly reliably.
Incidentally, if you watch their facial expressions, you get hints on whether they paid more or less than their Pin price. The expressions are a better tell than the dialog, because Woman, for instance, can give the same dialog for above-but-near and below-but-near.
EDIT: Note that if during the "main quest" you avoid meeting Euria, she won't pester you with her scams. You'll miss one dungeon this way, but if you can live with that until the last debt payment, apparently she never returns.
That's... very interesting. Maybe I'll try that if I ever restart again. You just don't go to the plaza events? Where did you find this out? Official forums, Steam forums, other location?
