Comment by ASalazarMX

Something that cafe "squatters" don't like to see: they're using a coffee shop as a shared office space, but gratis. The coffee owners tolerate this in exchange for sales, but the most egregious squatters will buy a coffee and let it sit for hours, and maybe go eat somewhere else when they get hungry.

Maybe a simpler solution is what I've seen some coffee shops discretely implement: chairs that are uncomfortable to sit for hours.