We used to have a really cute tip jar. It was a bank shaped like a kitty. Our customers found it confusing. They tried to take its head off. They struggled to stuff bills in the little slot. They turned it upside down and looked at it like it was a real puzzle.
A groomer friend from Canada came to visit and said, "You need a new tip jar. It needs to be clear, with a wide opening. Make it easy for people." We really liked our kitty jar, but put out this clear vase as an experiment.
The tips increased almost immediately. By a LOT. We keep a $5.00 bill in there as a gentle suggestion.
Another thing we did was change our credit card system to one that prints out a space for a tip, similar to the way restaurant slips do. In the past we might $20 a week on credit card slips. By adding this feature we now get hundreds of dollars in tips each week. We divide the tips between all the staff, but trust me when I tell you that this change has been an enriching one.
Bottom line is this... you need to charge enough for your grooming that you do not rely on tips. But make it easy for customers to give you a gratuity if they wish. And don't forget to say a heartfelt thank you when you are gifted with a tip!