If you sell items that can be dragged and dropped from the inventory to the ground and back, you can sell them more than twice
When it appears on the ground, drag it back into inventory before selling it again, and then it will appear on the ground again.
@Odie - I think I did read earlier that PI cases do count for opportunities
@geekchic - Use those pillow fight wishes to your advantage if you can - fight for a second, then cancel. Rinse and repeat until she's happy. If you already have enough LHPs, the fastest way is to take a potion of bliss - you can get one at the potion consignment shop, or make one very early on.