Responding to Garion Evans's questions

Voluntary exchange is two humans agreeing to trade, and involuntary exchange would be two humans trading on terms that would not otherwise occur without coercion.
Those definitions are pretty clear on their own, that's not where the problem is.

'Voluntary' can only be subjective, which means a 'voluntary exchange' cannot be observed, it is a belief held by an individual. Because of this, the term -cannot- be used to describe reality objectively, it can only be used to describe reality -as it relates to you-, from your perspective. The same thing applies to 'involuntary' or 'aggression'.

A series of examples dealing with aggression:

[1] Greg is walking down the street. John is driving a car. It's very cold outside, snow and ice everywhere. John loses control of the car after hitting some ice, hits Greg, Greg gets injured. John claims it was an accident.

[2] Greg is walking down the street. John is driving a car. John sees Greg. John really hates that Greg guy. John purposefully drives his car into Greg, Greg gets injured. John claims it was an accident.

[3] Greg is walking down the street. John is driving a car. John has been drinking heavily. John falls asleep at the wheel and hits Greg, Greg gets injured. John claims it was an accident.

Any of these events, besides a few details, are going to look identical objectively. Two people, one driving car, car hits person, person gets hurt, other person claims accident. The question of 'aggression' is answered based on perspective. Greg is experiencing the same injury although the circumstances around John's motivation and decisions leading to the injury are different. As third party observers, we can give our opinion on who/what is responsible for the injury using words like 'aggression' or 'accident' or 'unintentional' to make our case, but that's it.

A series of examples dealing with voluntary:

[1] Greg has $100 in his wallet. Greg is very thirsty. Greg finds himself at a movie theatre. The concession stand is charging $10 for a bottle of water. While Greg finds this price outrageous, his preference for satisfying his thirst is stronger than his preference for keeping his $10. Greg makes the purchase, fearing the consequences should he forgo drinking water any longer.

[2] Greg has $100 in his wallet. Greg is very thirsty. Greg finds himself at a movie theatre. The concession stand is charging $50 for a bottle of water. Greg finds this price outrageous, and in response he points a gun at the cashier and demands they charge no more than $10. The cashier submits to the demand, fearing the consequences should he refuse to comply. Greg makes the purchase.

[3] Greg has $100 in his wallet. Greg is very thirsty. Greg finds himself at a movie theatre. The concession stand is charging $10 for a bottle of water. The movie theatre owner would like to charge $3 for a bottle of water to maximize concession stand profits. Greg finds $10 per bottle to be outrageous, and thinks that $3 is a fair price. Unfortunately, the culturally accepted price of a bottle of water in the society they are part of is $10. If the theatre owner lowers the price, he will be ridiculed/excluded by his peers, friends, and family for his immoral act. If Greg finds and buys a cheaper bottle, he will be ridiculed/excluded by his peers, friends, and family for his immoral act. Both the owner and Greg do not question the $10 price, fearing the consequences should they deviate from the prevailing social norms. Greg makes the purchase.

Any of these events, besides a few details, are going to look identical objectively. Two people, one with a concession stand, one with money, bottle of water exchanged for $10. The question of 'voluntary' is answered based on perspective. Greg and the theatre owner are going to feel their decisions being 'forced' by certain circumstances.
Greg's thirst. Greg's gun. Culture. Possible exclusion by everyone.
As third party observers, we can give our opinion of how we would feel in those circumstances and then we can say 'voluntary' or 'involuntary' under that perspective, but that's it.
Some would argue that objectively [1] is voluntary and [2] is involuntary, but why?
In [1] if Greg doesn't drink water eventually, he's going to sustain injury, so to prevent the injury, he sacrifices his money.
In [2] if the cashier doesn't agree to the lower price, he's going to sustain injury, so to prevent the injury, he sacrifices his bottle of water.
"But in [2] isn't Greg threatening the cashier? Doesn't that make it involuntary?" Well why is a gun a threat? Because the cashier doesn't want to get shot.
This reduces to "But in [2] isn't Greg acting in a way that the cashier doesn't like? Doesn't that make it involuntary?" Well, in [1] isn't the cashier acting in a way that Greg doesn't like?
We can only make the distinction between voluntary and involuntary here by relating to either Greg or the cashier, then saying 'if I was in their circumstances, I would consider that voluntary/involuntary'. At the end, a judgement still has to be made based on -someone's- interpretation.

"See, that's what I want. A definition. Or a rubric. Something substantial. Otherwise people would just say that taxes are voluntary because of reasons and then the argument of voluntary = efficiency goes out the window."
"...what is a state and why aren't they as preferred by some people?"
"So then what's the divide between market and nonmarket?"
"I would argue that any non-voluntary transaction would be considered a nonmarket action, such as robbing a bank. But that leads me around in circles. I think Robert might be onto something with the idea of 'mutually beneficial' as being part of the definition."
"Oli, some people consider wage labor to be coercive. I disagree, but I'm looking for a more defined reason as to why. Time preference works, but I'm looking for the meat and potatoes."
"I like mutual agreement. But what's an agreement?"
"Then what's 'freely' mean? What can I point to and say 'that's voluntary' or 'that's coercion'?"
- Garion Evans

If you are looking for a way to identify the market, the non-market, and/or the state, independent of perspective then you are looking in the wrong place. If you use subjectively based abstractions like 'agreement' then your detection of the market will also be subjective, as in, your detection applies to you and only you. It will be based on your opinion and it will never be divorced from perspective. This is where 'muh coercive wage slavery' comes from.
I recommend that 'voluntary' is no longer used to -identify- a market. It leads to misunderstandings about what a market is when you try to communicate with people who don't have your same view of voluntary.
'Mutually beneficial' and 'free will' are problematic in the same way when attempting to use them as identifiers.

Businesses do operate differently than political organizations, they are driven by different demands coming from the public. If you want to distinguish market and non-market, I would start there.