I haven't seen too many blog posts on this. When I go out to eat at a place where there is a gratuity involved, I consider a gratuity to part of my expression to the kingdom of God in someone's life, especially if they give me good service. Its part of my silent giving that I give to give glory to God and encourage hard work and service.
My working base is 20%. If you give me average or slightly below average service, I'll tip you 15%.
Sheila and I don't go out often, but when we do, I am always prepared to give an extraordinary tip if I get extraordinary service: on time service, a smile, a warm greeting and a sense that you really want to serve me, if you anticipate my needs, my drinks, etc. Part of this stems from the reputation I've seen Christians develop, leaving tracks at times, with 10%, 5%, or even less than 5% for good service and the servers knowing these were Christians leaving the tip. Having worked in a gratuity driven economic environment for much of my adult journey, I have no place to put Christians who are so meager with their tips when they have been given good service, especially Christians who make their Christianity known to the server.
Tonight for our anniversary, Sheila and I went out for a nice dinner. I was prepared to give an extraordinary tip if I got great service. The guy was just an extraordinary server. Even though it was busy, he was right on top of us within a minute of us sitting down. Then he proceeded to give us great service the entire time we were there. He told us at the end that we could relax and take our time if we wanted to. Even though he had other tables, he gave us extraordinary service. When it came time to pay the bill, I gave him a 60% tip. I put it in the leather case holding the paid bill and left it on the table. He didn't see what we gave him for a tip. And, I don't have a problem if he never knows who I am or if I was a Christian. So, we got up from the table and we left. We were walking, holding hands outside the restaurant and we were about 50 feet from the entrance when we hear, "Hey folks!" We turned around and it was our server. "I had to come out here and chase you down and say thank you so much!!"

