Diablo – Should I repair the items before I sell them

I went to all available merchants in Act 2 (just in the camps though) and looked if there was a difference: There isn't. The selling price always is the standard price that you can see on items, even if you're not currently in a merchant dialogue.

If you want some real advice, though: The best merchants are players. If you're looking for good items, check the auction house. The items might be expensive, but you will get good items, and sometimes still for relatively low cost, way ahead of the quality that you're going to get from merchants (especially rares).

The same way, if you have any rares or other powerful magic items, rather sell them in the auction house than to merchants, unless you need the crafting materials.

Watch the auction house.

Right now, crafting materials are selling for substantially less gold than all but the worst low level blue items. You'll get far better results selling your blue items and buying Essences from the AH.

For example, current market value for normal mode mats is 20g for Subtle Essence and 45g for Fallen Teeth. So any item worth more than 25g, I sell. If its worth less than 25, I gamble for a shot at a tooth.