Easy 500 gems

In Louran, go to Temjin's house and talk to him. When he asks you what to do with his money, tell him to take it to his grave. Later on, when Louran transforms into a ghost town, go to the cemetary and check the most northwest grave. It's Temjin's. Guess what, the guy took your advice and you've just become 500 gems heavier.

Almost Free Saving and Inn in Litz

It normally costs you 10 Gems to get to the Diary in Litz, which is in the inn room with your bed. However, if you pay the man guarding the door for your room but never actually use the bed (use the food on the table outside instead) you can heal and save for free!

(Note: you will have to use the bed to trigger a cutscene after beating Bloody Mary)