Writer etiquette

When I write out of the house I want to go somewhere where I can camp (see previous post by that name) without getting in the way or pissing the staff off. I love our current venue but it does have a few drawbacks. The other week our usual spot was occupied but it wasn't a problem. This week same thing, only its a very drunk guy - passed out. His friends turned up later and in the end they all left together. We acknowledged them, it would be rude not to but I draw the line when complete strangers ask me to go shopping for them and they'll give me half what I spend in cash. I mean you honestly think I'm going to abandon my friend and go with three people I've never met. There's charitable and there's asking for trouble. So if you see a person writing in a coffee shop, by all means smile and if they say hi assume normal politeness rules so if they stop talking and go back to their work let them be, but never ever
a) ask them what they're writing
b) look over their shoulder and try to read what they're writing
c) ask them for a lift (yeah weird but it has happened)
d) ask them for money (the average writer is in as much fiscal distress as you are)
e) propose marriage (not cool dude, so not cool)