> As such, it also measures the income earned from that production, or the total amount spent on final goods and services (less imports).

It's my understanding that the "income" interpretation refers to tax income, because each transaction is taxed.

Take a look at your quote. It says it's also the "total amount spent on final goods and services". If you buy bread for 1€ and ham for 1€ and sell ham sandwiches for 6€, no one had income of 8€. At most, the state charged VAT on your 2€ purchases and 6€ sales.