Bring them back to your till for more time and more sales by using the coupon system. You can limit the time your customers have access to the internet, with a coupon provided with purchase. This takes the pressure off you or your staff dealing with ”long-time sitters”.
Let the software be the reminder that a purchase is required for more access time.
(Fun fact: some of our clients don’t require an additional purchase for a second coupon – but report that 70% of the time their customers purchase something anyway.)