The worth of an account is not going to be measured if you are a campaign manager or not, but I think it's based on the reputation that the person has built on that account and what the buyer thinks they can achieve using that account.
Hazink points out the obvious intention of these account buyers. They see the $10K as a fee to bypass a few years of building a positive reputation, so they must believe they can earn more than that. This can be confirmed if they asked philipma1957 to keep it quiet. The account owner decides if they can earn more than the offer and if not, the scummy ones may sell.
It's a "end game" scam that cannot easily be prevented. Once the community realizes the accounts has been sold they tag it, but by then the scammer and account seller have taken their profit. Obviously accounts like philipma1957 and Vod go for six figures because we have earned overall trust here, whereas the most recognized scammer accounts won't draw much attention. I just hope this doesn't turn into a contest of "I wouldn't sell MY account for 5 bitcoin!", because remember people can post anything.
Expired accounts, like o_e_l_e_o, will also never sell, even if they are owned by a living person. People know it would not be him.