Nice graphical breakdown.
I think the real winner isn't Bob or Alice though they each benefited from the exchange. The real winner is the credit card company that banked 10% of the transaction on Alice's side and 5% on Bob's side. Sounds like they both chose the least sensible option to handle payment.
Maybe Bob should've made it clear that he accepted cash, money orders, cashier's checks, or personal checks, or even cryptocurrency so that Alice would not need to suffer a foreign currency conversion fee especially when you consider that they live in the same small town.
Just kidding. I realize that the example transaction needed some massaging on the path to the end graph to illustrate handling of more complex, real-world transactions.
Great job producing this intuitive break-down.
There is one thing that I found interesting near the top of the tutorial. You make the statement "But money is meant to be spent." If money exists to be spent then why do so many people accumulate such vast sums that they could never spend all that they have managed to accumulate? Dumb question, I know. Money in the hand has indeterminate or no value until the bearer needs to acquire a product or service and then the value of the money in hand is set by the seller of the product or service they require. The global economy functions because at some point in time a traditional barter system where useful physical items were exchanged was replaced by the current system involving exchange of special artisan linen papers or conveniently portable metallic disks emblazoned with cartoon images celebrating historical events or personalities.
Anyway, this was a good read and I enjoyed watching the transaction ledger complexity increase to account for real-world situations where there are more than two parties involved in a single transaction. Years ago when I was in high school we had a class that introduced us to checking and saving accounts and the goal of the class was to teach us how money moves through the system so that we could manage our own assets once we had real jobs and incomes. We had the introduction to the ledger book with one side handling credits and the other handling debits. It was all confusing at first but ended up being very useful.
A long time after this class I found myself working as an independent consultant paid a negotiable hourly rate. All of that earlier instruction came in very handy when I needed to split project time and classify and categorize all the transactions that helped me understand where all that cartoon cash came from and where it all went. My spouse is a CPA/Auditor so having her level of knowledge and experience close to hand was also enormously useful in splitting everything so that the charts and graphs I assembled were most intuitive.
Thanks! I enjoyed reading this.