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.