@xo1 your example/analogy with the used car is, actually, flawed
Miles will reduce/depreciate the original value of a car. So, if life expectancy of a particular car is 40,000km, then in fact a car with 20,000 miles would be twice as valuable. But, that's totally besides the point.
The point is, advertising is almost always priced based on a CPM. So, the greater the engagement/reach, the more you are going to make selling advertising. Therefore, account with twice as much reach 'should' be worth twice as much In reality that may not always be the case, and there are other particulars, such as niche, the influential value/extent of a particular account, etc.
The labour that went into building this account to 208K followers in the past 3 years far exceeds the $20K asking price. That's because every single follower on this account has be earned by posting quality material. No shortcuts were taken and the engagement is proof of that.
To those that do not appreciate true/generic and quality account, I would advise to just simply skip this thread/topic, and move on with their lives... as simple as that