The trick with tricking your own brain is not to make something impossible. It is to make something annoying enough that you have time to consider not doing it. For your specific example if I struggled with buying too many things on Amazon I would probably attempt the following (depending on how pissed at myself I was). Each assuming the previous has failed to curb the behavior

uninstall the app
block the site using a browser extension
block the site in my router

Nothing stops you from undoing any of these other than how annoying it would be to undo it. Hopefully by the time you are half way through undoing it you realize you don't actually need a new guitar pedal. You just want to enjoy your hobby again so maybe it's time to join an online community

But like with all things in life, experiment and find what works for you