There are many ways to arrange a TF* shoot, but to avoid over-complicating the situation, let’s just stick with Trade For Images/CD/Prints, because that’s the most common form of TF*. Working trade, or TF*, means that the parties who agree to work on a trade basis are both going to benefit from the shoot. It doesn’t necessarily mean they are benefiting from the same shots from the same set they shoot, but regardless, they are both getting work they can use for their portfolios.
In the case of working trade, the photos received after the shoot are viewed as fair and equal compensation. They may not have specific monetary value (meaning you can’t pay your water bill with a photo you receive from a trade shoot), but they have value in the sense that they can be used to improve portfolios and (hopefully) further careers. In theory, if you wanted to attach a dollar value to a trade shoot, you could say the model posed for $50/hour, and the photographer charged $50/hour for the studio session and retouching services combined, so the two values canceled each other out.
Trade agreements are often individual things, and vary per shoot, per person. There are largely no rules when it comes to trade shoots. That is, discuss all trade agreements in advance prior to working with someone, even if it’s someone you’ve worked with before, to ensure you are properly compensated for your time, and vice versa.
Typically, if one party cannot benefit from working with the other, it is such that they ask to be paid in order to be properly compensated for their time. If, for whatever reason that person chooses, they opt to not have money exchange hands, they would then be working for free. The party who will not benefit from the shoot, but is not asking for monetary compensation in exchange for their time, is donating their time and experience, knowing full well that they will not benefit from the shoot, nor will they receive fair compensation for their time.
Now, it’s possible that someone who works for free can benefit from the arrangement. After all, it’s likely they will get a positive review from the person they worked with, and might therefore have others interested in hiring them. But generally, those who work for free do not count on this happening. Which is largely why many do not work for free, but instead opt to trade with parties that will benefit their books.
“Free” is not the same as donating time to a charitable cause. That’s entirely different, and not something I’m discussing now.
More often than not, when one party will not benefit from working with the other, the non-benefiting party will send rates. By applying their rates to the shoot, the non-benefiting party is receiving fair compensation for their time, since they will not benefit from the images they receive from it.
If someone quotes you a rate, it’s not cute to quote them a higher rate back and say “ha, look at that, my rates are higher, so you pay me”. Chances are, they sent you rates because don’t think you’re worth working trade with. If working trade with you won’t benefit them, chances are, they’re not interested in paying you.
Let’s note that I haven’t once mentioned the amount of money any of the involved parties spent on gear, training, gym memberships, wardrobe, or any of that BS. It’s not relevant.