Yes! You can let clients add a tip to their payment when booking online. Full Slate's online payment feature lets you accept payments from clients when they book appointments online. With this functionality, they can add a tip to the price of the service and the combined cost will be charged to their credit card.
The tip option will only be presented to clients when they pay for the appointment in full. Also, if you use Paypal Checkout Express, tips will only work if you require clients to pay online (i.e. it will not work if payment by clients is optional).
Your clients can then relax when attending their appointment with no worries about payment.
To enable tips, simply check the "Accept tips" box under Setup > Client Payments.
Please note that when tips are enabled, clients will also be able to add a tip when buying gift certificates online if you use Stripe, Authorize.net or Paypal Payflow (but not if you use Paypal Checkout Express).