I know that for many, and most, countries tipping is not expected. Rather, the employer pays the deliverer better base wages.
It's a nice way for businesses to reduce overhead by shifted burden on to the consumer. If the tip is high or low, the employer wins either way. The consumer has lower base prices due to lower overhead of employers, though with a added tip, the cost is either a bit lower, the same, or higher, and lastly however, the service person is left in limbo (and thus it's assumed they will work harder to better their predicament.)
If this is the system of tipping, and we maintain this system is established for the purpose of improving service industries and effort-based pay, is it not better as a consumer to actively vary tip based on performance?
It seems like there are low-tipping consumers and high-tipping consumers, who tip fairly the same regardless of the performance of the service person. In that case, does this negatively impact the service industry? As a consumer, do we affect other consumers by the way we tip?
That is, if I give a high tip to a low-performing service person, does that encourage low-performance to the next consumer? Similarly, if I give a low-tip to a high-performance service person, does that discourage workers from continuing excellence and sense of job security? As you can see, there are negative implications to both consumers and workers.
That is the argument to be made for varying how much we tip. Though, abolishing the custom of tips all together might be a better solution, though I am not prepared to argue either side.