Sure there are instances where people will sell their accounts plus their private keys however trying to scam with a trusted account is a gamble at best and a gamble with small potential rewards and high risk and a generally small success rate. I would call the EV of buying a trusted and/or a default trust account to be negative by a long stretch.
It's impossible to calculate without real, actual, values. The value of the default trust account to someone who's going to be walking away from the forums forever (for any imaginable reason) independently of whether they find a buyer is whatever they can get for it. Ie, if you know you'll never use it again, then you've got every incentive to sell for whatever you find someone willing to offer.
It's impossible to say what the value of something is/isn't without knowing actual details of a given situation. Anyone who says otherwise is engaging in mere speculation---this can be fun, but it's not solid argumentation.
I know what people are generally willing to pay for default trust accounts, how much default trust accounts have sold for in the past, I know how much people are generally able to hold for a third party before suspicions start getting tripped.
It is pretty rare that someone attempts to use a purchased account to scam many people for as much as possible however in almost every case that I have seen the amount scammed was significantly less then the value of the account and in cases when the amount scammed was greater then the value of the account, it was because one person who doesn't know how to take proper precautions got scammed for a large amount.
Your argumentation basically boils down to
Argument from authority, which is a logical fallacy.
The starting point is the assumption that you know the value of the account
to the seller, this is obviously highly dependent on the person and their circumstance.
[inb4 ad hominem attacks: next, QS either calls me an idiot or doesn't reply at all...]
It could be worth 1 btc for example but the owner only values it at .75 btc, they obviously won't sell it for the lower amount, conversely if someone wrote to value their account for 1 btc but the market would only support a value of .5 btc then the account would either not sell or would sell for less then what the owner values it at.
You say it does not matter but then you go on to show exactly how it
does matter. Both buyer and seller have to agree if there is a sale to be made. If I value my account at X, then I won't sell lower than X. That is exactly what you go on to say. So, again, it's impossible to see how much a person would sell a (default trust) account for until someone actually puts a price on their (default trust) account. You can't really say what the "value" of an account is independently of actual data. This fact impunes your reasoning when you say "the value of a default trust account is always negative"---this clearly depends on the price, which you don't know until someone makes an offer.
My point is that the value of an account of ultimately determined by the market. People can give a value to their account if they want however any rational decision will be based off of market prices.
This matter is independent of theories of (ir)rationality. You don't know the "market prices" until a sale goes down.
BTW, good job holding back on the insults! You're making progress, it seems.