I have a colleague that has a job he took on, and has asked
for my help. The job requires a "shopping cart" to be built,
but using the existing site architecture. Which means we can't
put up an open source cart, like oscommerce or others.

Not too hard, as the site is selling broadband packages.
Simple PHP functions have to be written to take all the options
and prices for those options from forms - and calculate them
in a "sidebar" calculator that displays the customers orders
for them every step of the way.

Problem is, at least for me, that will take a lot of my time,
time I spend trying to make money to pay my rent! This is a
non-paying job. The client of my colleague says he'll "refer"
us if he likes the work.

Now, referrals would be great!!!! but they are not guarantees
of work. So I'd like to ask you all if you do "intensive work"
for free, with just "word-of-mouth" as payment?