The easiest and quickest way to make money is on Chapter 4-1. When it dies you can collect the Soul Gem which is worth 10,000 gold when sold. Just continue to walk backwards around the pillar and attack with whatever you have when it is vulnerable, shooting the soft portion on the back of its tail. The "Dodge" button will appear, but it is not necessary. When Sheva tells you that it is too hard to fight and you should go upstairs, if done correctly you can just walk backwards without having to dodge around the pillar as the Boss tries to attack you. In the southwest corner of the bottom floor, there is a small pillar of stone in the middle, with what looks to be a log with spikes coming out of it as well as a rib cage hanging from it. When you face the flying bat/insect-like creature for the second time in Chapter 4-1, there is an easy way to defeat him which will allow you to still get the Soul Gem. For example, it does not matter which pistol to buy, as long as you are trying to get pistol ammunition. However, when you sell the gun, whatever ammunition inside it when being sold is be transferred to your inventory, allowing you to "buy" ammo, albeit at a very high price Note: Buy the lowest cost type of gun because the ammunition is universal.
If you have a lot of money, and have unlocked a particular gun, you can buy that gun and sell it for a very reduced price. Mercenaries mode: Getting better ammunition.Easy "Who Do You Trust?" achievement or trophy.Easy "The Works" achievement or trophy.Easy "Masters Of Removing" achievement or trophy.Easy "Go Into The Light" achievement or trophy.Easy "Egg On Your Face" achievement or trophy.Easy "Egg Hunt" achievement or trophy.Easy "Bull's-Eye" and "Crowd Control" achievement or trophies.Easy "Bad Blood" achievement or trophy."Uroboros Research Facility": Easy ammunition."Civilian Checkpoint": Hidden dialogue.