Where is the risk with a? Seems like you yourself explain why it would work fine. If you get the coins, great. If not, you do a classic charge back. Either way

Where is the risk with a? Seems like you yourself explain why it would work fine. If you get the coins, great. If not, you do a classic charge back. Either way, trust of everything outside of owning your coins is irrelevant to the exercise. If you're going to play devil's advocate, you need to come up with relevant counter examples.