I do freelance work for a full color magazine. The magazine is a
startup and haven't been able to pay in full for my work. The want to
trade services from their advertisers, to knock down my bill. My
question is what is a fair trade value for something I don't really
need, but will take as payment. An example is one of their advertisers
is a eye doctor. He will give me glasses for $150. I don't really need
them, but I will take them. Now how much to take off their bill? What
is a fair trade rate for something I don't really need, but will take
because I need to get paid somehow? Please Help!

Glasses @ $150 are a complete ripoff, especially if you don't need them.

Here in the UK, reading glasses can be bought for less than $2 (but
not from eye doctors) and I guess the same is true in your neck of the
woods.

Rule 1: Only take stuff you need;

Rule 2: Only take off the bill whatever it's worth to you.

You've got to be hard!

Good Luck!

Bryan

There are some swap clubs.  See how they value things.  

Might be a place to "sell" multiple pairs of glasses as well.

There is another angle here
- the magazine is offering you an intro to their advertizers
- that is potentially useful, the eye doctor probably needs
promotional material and things like letter headings.

Obviously it would be annoying to be paid in spectacles, and this
might set up bad habits, on the other hand, if you got $150 vouchers
from him that you could sell to other people for $100 ...

If the publisher get's the eye doc to give you glasses for 150$,
what's the problem of making a direct money exchange - that's what
it's there for.

I tried barter for my labor once. It was extras work. Paying in cash
is easier and does not complicate your life. Typically you can get an
adjustment if you feel cheated, but it is less probable with barter.
IRS may audit you if they suspect you under reported your gain.   Neil