NetLogo permission oddities - permissions

Question

I'm having issues with my netlogo program. Code follows:
globals[
growth-param
money-size-ratio
]
turtles-own[
location
tsize
bbalance
]
to setup
ca
reset-ticks
ask patches[set pcolor blue]
create-turtles initial-telemarketers [
set size 1
set bbalance 0.0
setxy random-xcor random-ycor
set shape "circle"
]
set growth-param 1000
set money-size-ratio 0.001
end
to go
ask patches[set pcolor blue]
sell
accounting
observer-updates
tick
end
to sell
let territory 10 * sqrt size
let maxcalls 100 * size
ask n-of maxcalls patches in-radius territory[
if pcolor = blue [set pcolor black]
set bbalance bbalance + 2
]
end
to accounting
let cost size * 50
ask turtles[
set bbalance bbalance - cost
ifelse bbalance < 1
[die]
[set size bbalance * growth-param]
]
end
to observer-updates
end
It's supposed to be a model of how many telemarketing companies interact, simplistically. It's from Railsback & Grimm's modeling book.
Each time it tries to run, it provides two problems that I can see: in procedure sell, it doesn't want to set bbalance to the new value because it is turtle-only, and tick is observer-context only.
Thanks for any help!

Answer 1

globals[
money-size-ratio
]
turtles-own[
location
tsize
bbalance
maxsize
]
to setup
ca
reset-ticks
ask patches[set pcolor blue]
create-turtles initial-telemarketers [
set size 1
set bbalance 0.0
setxy random-xcor random-ycor
set shape "circle"
set maxsize 0
]
set money-size-ratio 0.001
end
to go
ask patches[set pcolor blue]
ask turtles [sell]
ask turtles [accounting] ;; let's ask the turtles to do this
observer-updates
tick
end
to sell
let territory 10 * sqrt size
let maxcalls 100 * size
if maxcalls > 40401[
set maxcalls 40401;keeps maxcalls within acceptable bounds
]
let coun 0
ask n-of maxcalls patches in-radius territory[
if pcolor = blue[
set pcolor black
set coun coun + 2
]
]
set bbalance bbalance + coun
end
to accounting
let cost size * 50 ;; size is a turtle variable so if you want to access it this way, let's make the whole thing
;; a turtle procedure. That's what was confusing Netlogo about the tick command
set bbalance bbalance - cost
if bbalance > growth-param
[set size size + (bbalance - growth-param) * money-size-ratio
set bbalance growth-param
]
if size > maxsize[
set maxsize size
]
if bbalance <= 0
[show (word "dead. Maximum size: " maxsize)
die
]
if size = 0
[show (word "dead. Maximum size: " maxsize)
die
]
end
to observer-updates
end

Answer 2

sell is a turtle procedure (because it uses turtle primitives such as size and in-radius). But go is an observer procedure. You can't call a turtle procedure directly from an observer procedure; you need to specify which turtles you want to run it. Inside go, I think you may have meant to write ask turtles [ sell ] instead of just sell.