Don't know why it's a good spot for fishing but I think they actually aren't paying much attention.
Apparently they fish for Carp - asked them last time I went for a therapeutic massage. Not a fisherman so I don't know how edible Carp are.
Suppose they could be undercover surveillance, watching how happy those coming out seem to be. 
I don't think you'd want to eat anything that came out of that dock.
There used to be a sign on one side of the dock that proclaimed that the fishing rights were 'owned' by some angling club who issued the licences.
Some nights they camp out in tents, I don't want to think about where their waste goes!
Apart for something to gossip about, I doubt that they have any interest in the comings and goings.
Add to that, like the bus stop crowd, I doubt they have much understanding of the two side of a Thai Massage business. At the gym I use there are often signs offering specal deals and discounts on Massage Treatments and I can't thinik that it is anything but straight. Massage treatments are quite normal in the public environment nowadays, even available on the NHS. It's only because you know what is being offered and what you are expecting that makes you concerned.
