One reason for tips not being put on the credit card, or any card is usually the stylist has her own chair. She rents chair or station. She can use the salon to run charge through, minus the tip. If they added tip in it would look like the salon was making more than it does.
They could do extra book work, separate the tip from amount service, but it is a lot of work.
Also, every time you use credit card, or debit card there is a fee to salon. It is part of doing business. But to add tip onto service, 3% or so would be take out for fee.
most salons keep all charges separate. They are not paid hourly. I have been in many salons, and spas, that have a separate tip drawer. When tips are not given directly to stylist, they are given end of day, or next day. Many salons collect the tips, and report it to IRS that way.
in some devious salons when tips were added to credit card, stylist never got them or the owner took a cut of tips before giving to stylist.
most tips are reported. IRS knows you are in a tipping business, they expect a certain amount of wages to be tipped.
where my granddaughter works. All tips by credit card or cash go through main cash register with your name on ticket. She picks up her tips next work day in cash. The management reports all tips to IRS.
I can tell you the number one reason for cash tips is book keeping. They might not report a few bucks, but most are reported.
“sometimes you have to bite your upper lip and put sunglasses on”….Bob Dylan