After some weeks of trying to find a good balance between profit and the time you have to have your stall open, I've come up with a very basic formula that works rather well at least on Athens.
NPC = NPC selling price = the price you get when you sell the item to an NPC.
Base price: 2 x NPC
AdditionsINT or STR +1 = 0 x NPC
INT or STR +2 = 1 x NPC
INT or STR +3 = 2 x NPC
INT / STR +1/+1 = 1 x NPC
INT / STR +1/+2 or +2/+1 = 2 x NPC
INT / STR +2/+2 or = 3 x NPC
INT / STR +2/+3 or +3/+2 = 4 x NPC
INT / STR +3/+3 = 5 x NPC
+1 = 1 x NPC
+2 = 2 x NPC
+3 = 3 x NPC
+4 = 4 x NPC
etc.
Critical < 5 = 0 x NPC
Critical 6-7 = 1 x NPC
Critical 8-9 = 2 x NPC
Critical 10-11 = 2.5 x NPC
Blocking ratio < 14 = 0 x NPC
Blocking ratio 14-15 = 1 x NPC
Blocking ratio 16 = 2 x NPC
Blocking ratio 17 = 2.5 x NPC
Blocking ratio 18 = 3 x NPC
ExampleYou have a blade with an NPC selling price of 10k. The blade is +1 and STR +2, with a Critical of 8. I would sell this for:
20k (base price) + 10k (+1) + 10k (STR +2) 20k (Critical 8 ) = 60k
This is of course not a perfect formula, and it might not work for you, and I'm sure you could sell the items for more money, but like I said in the beginning, this is for me a good balance between the profit and the length of time I need to have my stall open to sell my items.
Anything without bonuses I sell to the NPCs; the same goes for everything that is just INT or STR +1. It's not worth the time to try and sell it in a stall unless you have a dedicated shop character.
Again, I'm not saying this is the only way to price items, but feel free to try it out if you want. Any and all feedback is appreciated and most welcome.