Note: This game is also titled Rune Factory: Oceans.
Successfully complete Lily's first request to get some money for this trick to work, and make sure someone is selling items at the bar (preferably Lily or Electra for the access to Ice Cream). Buy all the milk possible for 120g. Cook it into hot milk at the inn's kitchen, then sell it back to the store for 200g. You can buy Ice Cream as needed to replenish RP. Repeat this as many times as desired. Note: This trick can ruin the game somewhat because on the very first day you will easily be able to afford all house upgrades, armor, weapons, crafting material, and medicine. Additionally, you will be doing this trick at the inn where time will not pass while doing it.
Accept any Bulletin Board request that gives you an item before completing the quest, such as a Delivery quest. Talk to the person who requested the quest, and get the item. Then, cancel the request, and accept it again to get another of the same item. Repeat this as many times as desired, then sell all the items. Note: Do not complete the quest until you get the desired number of items from the quest.