Thats not an authorization, they took advantage of you. You do not have to be an expert on your vehicle, the maintenance of your vehicle is a business transaction and you should treat it as one. Know what is needed from the scheduled maintenance section of your owners manual.
Knowing what is needed ahead of time, you go in and ask for an estimate for these parts and services, in business terms you are submitting a request for proposal (RFP). They respond with the estimate, in writing, aka the proposal. If you accept the proposal/ estimate, you sign and they begin work.
If inspections are part of the estimate and they find something that needs additional maintenance, then they must call you for approval. They should give you an estimate for the additional work as well, but you should ask for the urgency of the job. For example, your brake pads may not have been urgent. They may have had a few more thousand miles left on them so you would have the option of having the brakes scheduled for a later date or you could get estimates from other shops.
Its business, plain and simple. You were taken advantage of by poor business practices. They may be good mechanics, but they are not very ethical when it comes to business. At least based on what you have told us so far, there may be some extenuating circumstances due to a misunderstanding between you and them.