I can't even sell stuff that's in the regular shops.
I grew up as someone who takes the small victories, so if I think I can get even 10k more if I wait instead of selling now, I'll wait.
But then I realize I really like the item (I bought it in the first place, right?) and never sell. I suppose that makes me a hoarder, but when you can't really replace what you have that often it makes you cling to those that may give you the most bang for your buck. I tend to not use items for months and then feel like using it, so I make an outfit around it.
Rinse, repeat with different items every time.
I've stalked the MP for days when buying even cheap items so it's no surprise that it takes me longer to decide on selling it, no matter how profitable.