The other question of course is what would someone be doing here 90 days at a time all year long?
Why wouldn't they just get a work visa or HK ID, and if that wasn't the reason, who does "Visa runs"? And why?
Are there people who should be getting visas that aren't? Because if they are staying 90days they are contributing to HK's economy in some way that's for sure, would someone do this purely to avoid tax, I cant believe.