If you never authorized the work, then no in theory you should pay for it. The reason I say "in theory" is that if you accept the work--such as by keeping the new brake pads, and they are demonstrably better and more valuable than the old ones--a case could be made that you'd at least need to pay for the part, if not the labor.Another issue is that if there was a legitimate difference about what was said or authorized (e.g. the mechanic thinks you said just "take care of the bike" and took that to mean to make necessary repairs or maintenance), it could be difficult to prove you position in the event that the shop or mechanic tries to put you in collections or sue. You need to decide what not paying is worth to you.If the work is good and the price fair for it, you  may wish to consider paying (possibly seeing if you can't negotiate down some) but then finding a different mechanic for the future.