Four ways my subscription scanner was wrong

I wrote the first version of Billio's Gmail scan, ran it on my own inbox, and it found nothing. Then I loosened it and it found too much. Here is what went wrong, in order.

It found nothing

My first rule only accepted senders I already knew. Real inboxes have receipts from services nobody would think to list, so I let unknown senders through when an email looked like a receipt.

Then it found food orders

After that change, my food delivery orders showed up as subscriptions, and only one result in eight was right. Those emails say receipt and thank you, just like a subscription does. Unknown senders now need stronger evidence, such as the word renewal, a next billing date or repeat receipts, and order and delivery wording rules an email out.

Apple hides the real app

Apple sends receipts for many apps from one sender, so everything arrived looking like one subscription called Apple. The app name is inside the email body, so Billio now reads it from there. A friend then tested it, and his iCloud invoice slipped through because it is laid out differently, so iCloud and Apple Music are now matched by name too.

A dollar subscription filed as naira

One subscription was billed in dollars, but Billio showed the amount in naira because it assumed the local currency. It now reads the currency from the email and lets you change it.

The lesson was the same each time: a test on my own inbox is not a test. The bugs showed up when people with different inboxes tried it, so I keep asking friends to run it and send me what went wrong.