There is no implied service contract when it comes to tipping.
An implied service contract is a legally-enforceable contract. For example, if you went to a barber shop and sat in the chair and the barber gave you a haircut, then it is implied that you will pay for the haircut. Theoretically, the barber could take you to court if you refused to pay, and the barber would win.
A tip, on the other hand, is gratuitous. The server performs their service in the hope that the customer will give a tip, but there is no obligation for the customer to do so. If a server tried to take a restaurant patron to court for not leaving a tip, he would lose.
There is no implied service contract when it comes to tipping.
An implied service contract is a legally-enforceable contract. For example, if you went to a barber shop and sat in the chair and the barber gave you a haircut, then it is implied that you will pay for the haircut. Theoretically, the barber could take you to court if you refused to pay, and the barber would win.
A tip, on the other hand, is gratuitous. The server performs their service in the hope that the customer will give a tip, but there is no obligation for the customer to do so. If a server tried to take a restaurant patron to court for not leaving a tip, he would lose.