I may not be entirely or even slightly right (so any staff who know better than me, please feel free to correct) but my knowledge of how purging/selling new usernames is this:

* Person buys rename token for specific username which has been purged
* DW staff see rename token and manually change the purged username to something else non descript so that the usernames of comments change
* DW staff assign purged username to person who bought

This process is the same, irrespective of how the purged username was once used, or how it is henceforth going to be used.

i.e. it requires person-power to do some work and therefore, you have to pay for that.