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Before he orders his meal, he places a neat stack of $20 in singles on the table, catching the attention of the staff. After he orders, he tells his server that the $20 will be their tip if he is satisfied with their service by the end of the dining experience.

If he isn’t satisfied, he will remove a dollar or two, or more, from the stack of bills for every perceived infraction or obvious mistake. For example, if the server doesn’t return in a timely fashion to check on drinks. Or if the kitchen staff doesn’t get his order correct.

Otherwise, that $20 would remain untouched and left for the server, even if the total bill was $30 or $60.

“You’d be amazed how much it improves the service at my tables,” he often told me.Ěý

I never had the assertiveness to try it. Like most people, I gauge my tipping metrics on an odd criteria of factors beyond taste, speed, friendliness and cleanliness, such as a server’s attitude, time spent at my table and other intangibles.

An interesting study explored the connection between non-service interactions between waitstaff and customers, and the size of their tip or gratuity. Researchers looked into why patrons are tempted or enticed to leave a bigger tip than the standard 15% or 20% or more.

The study’s premise was simple enough: What motivates someone to tip more when they have no continuing relationship with the server? One of the most important factors is developing a relationship with a customer, even if it lasts only a few minutes and in between drinks, meals and desserts.

In one experiment, restaurant servers found that if they gave pieces of chocolate to dining parties after the meal, their tip increased from, say, 15% to 18%. Researchers concluded that reciprocity — the motivation to return the good deed of the "gift" of chocolate, no matter how minimal, by tipping more — was the likely explanation, according to a compelling story in The Washington Post.

Other experiments for the study found that if a server writes "thank you" on the dinner check, tips go up two percentage points. This technique definitely works on me, especially if a smiley face or first name is next to the “thank you.”

These are additional factors that help boost tips:

• Writing something about nice weather on the bill (an increase of 4 percentage points).
• If a female server touches a customer's hand (increase of 5 percentage points).
• If a server introduces herself or himself by name (a gain of 8 percentage points).

Those additional gestures add up, though it shouldn’t come across as forced, fake or manufactured simply for tips. The study concluded that actions and situations boosting a customer's mood prompts them to tip more. Makes sense to me, but possibly not so much with younger customers, according a Bankrate survey released this summer.

It revealed that members of Generation Z, born in the late 1990s and early 2000s, are the least frequent tippers at bars and restaurants. In my younger years I was a poor tipper though I worked for 20 years in the food industry, interacting every day with customers.Ěý

For me, it was strictly a matter of financial means. I didn’t have much money to spare, so I tried to compensate by praising servers and other restaurant workers for the job they did. As a worker, I valued this sort of alternate compensation from patrons. I preferred cash, but I appreciated kind words for what is typically a thankless job.

As I got older, my tipping increased, but I’m not as generous as I could be. Tipping etiquette calls for giving at least 18% to 20% these days. Anything less is either a reflection on the service or the customer. I’ve given some servers 30% or more, but it often reflects my mood more than their efforts.

"Tip creep" is rising at restaurants, bars and other service industries. Customers are expected to contribute more to workers' earnings.

But I sometimes hesitate to tip for carryout pizza, which I order consistently from restaurants. Last month, I picked up a pizza from Lou Malnati’s on State Street in Chicago, where the employee behind the carryout counter flipped the screen toward me so I could add a tip, or not.

“No obligation,” she told me with a smile.

I added a 15% tip based on her attitude more than her role to hand me a pizza. For me, the secret ingredient to earning a higher tip is to make a personal connection on a human level. If it's genuine, even better. If I can't tell the difference, they deserve 25%.