Update - I paid 15%. Felt kinda guilted into it; when the credit card was swiped, I had the "option" of adding a tip. It came to a gratuity of a little over $30 on a six-treatment package, so not the end of the world, and the tech who performed the first treatment was extremely patient with me and certainly earned the money.
On a related subject: my god, that laser f**king stings a million times worse than I ever expected it to!
