This Seeking Tech guide will explain how you can get infinite Pesetas in the Resident Evil 4 Remake as well as the Separate Ways expansion.
For this glitch to work, you need to take the following steps:
Use the following video as a visual aide:
Step #1: Have at least 3 First Aid Sprays.
Step #2: Have 1 First Aid Spray in your Case and put the rest into Storage.
Step #3: Talk to the Merchant and go to the Sell menu.
Step #4: Make sure that the First Aid Sprays in the Storage is listed above the First Aid Spray in your Case.
If it is wrong, randomly remove/add weapons (including Combat Knife) to your Case until the storage sprays are listed above the case spray.
Step #5: In the Sell menu, add all First Aid Sprays from Case and Storage to the sell order.
Step #6: Open and then close the Case from Sell menu.
Step #7: All the First Aid Sprays should now be transferred to Storage. Sell all of them.
Repeat Steps 5, 6 and 7 to infinitely sell First Aid Sprays for Pesetas.