My father and I co-own three car washes. What we pay our self-service attendants depends on their skillsets. For instance, someone who is what we call a body (an attendant with no mechanical ability) is paid $11, Maryland's minimum wage. Our mechanically inclined attendants make $14/hour.
Our mechanics make anywhere from $20/hour to $40 and hour, again depending on skillset. Our computer guy gets $40 an hour because he's the only one in the bunch who knows the computer aspect.
Our self-serve attendants also oversee our IBAs, and they do get $10 commission for when a new vehicle signs up, followed by $5 for additional vehicles the same person does.