Yeah, I get the concept of negotiation, but practically speaking how are photographers or models approaching it?

Photographers:
Are you basically saying, you'll only pay someone if you have to?
You really want to do the shoot TFP but no one responds to TFP calls so this is a way to get people to answer in that they hope to get paid?

Models:
Do you more often respond to a casting call that's negotiable vs. tfp?

I think a lot of people are fishing.  I come from the photographer side.  I pay my models almost always.  Most are starving students so it seems fair.  But I pay modestly.  So I ask someone to pose for me, she cites rates that are three times what I pay.  I used to tell her what I pay, and then she says that because I am such a sweet guy, she will work for only twice what I normally pay.  The problem with this approach is that I am not buying fruit in a market where once the price is decided I walk away, the seller is more or less happy, the buyer is more or less happy.  No, once the negotion is finished, that is when the work begins.  And, unfortunately, when I have gone through that sort of negotiation, then there is too often a lot of attitude left.  Maybe I am imagining things but I get the vibe that she is not into the photo session, that she is doing me a favor.  The vibe in a session is important to me.  I produce better results with an unremarkable model who loves my work and wants to pose for a silver print than a model with an awesome bod who thinks I am just another source of cash.  I am not sure this is too the point of our post, KM.  But in my experience, there are 3 to 4 back and forths on the reasonableness of an offer, but I avoid it now.

If I put "negotiable," it means, "I want a model for this. If you want prints and files, then I expect to pay you less than I would if you didn't get prints and files." "Less" can include "not at all." Depends. If the model will pose for my heart of stone project (requires at least sheer nudes) and doesn't want any prints or files, I pay her. If she will  and she also wants some prints and files of the shots, I pay her less. If she will and she also wants prints and files of headshots or lifestyle shots, then I probably wouldn't be willing to pay her anything, as I'd view that as a trade.

M

To means, that I want to be paid BUT if you can offer me something like a tearsheet or something else that is of value to me, I'm down.

...Basicly that I'm not a hard ass with everything set in stone. It says " Hey, I'm reasonable"

When I post castings using it.

It means.
I need someone as in the shoot NEEDS to get done.
What is given as far as edits,  money, access to images,  etc or what rights I want are up for negotiation.   The person is question is welcome to send me what THEY need out of the shoot.
To send me their price.   This is higher than a  free shoot or TFwhatever for I do not want to drop the idea of the shoot.

It is not placed as Paid for the price is not fixed yet.  Likely coming out of my pocket and yes,  I would rather not have to pay or give away the house to get the shoot done.

This goes both ways for I have ideas where I would love to have a stock release for certain images.
But I likely want to shoot the idea regardless of if I get this release.  Money and/or prints delivered within a shorter time period which likely means my not printing or editing myself.

As with all things,  I base my judgement on what is in front of me.   I take the best person based on the information in front of me.

Would I like to shoot Kate Moss with Nico doing the styling for free?  Sure,  but if Penelope Tree wants to travel in a time machine and have Cleopatra style the shoot with items from her showroom well then I will shoot  Penelope instead.