they are punishing link sellers (and possibly buyers)
That may be what they think they are doing. I am neither seller nor buyer, and I know my site provides quality content from the amount of time I have to spend pursuing copyright infringers. Similarly, having returned first-page results for a high number of sector-specific terms for the best part of a decade, my site has acquired a lot of backlinks (mostly - because I have been careful to ensure titles, descriptions, urls, etc, accurately reflect content - using page topics as anchor-text). If staying in Google listings means scrapping that way of working, then I, for one, will not recover from Penguin.
One might forgive the odd mistake if the results were now filled with better quality, higher relevance, or less spam. They are not. Penguin doesn't seem to be able to tell a genuine link from a stuffed aubergine, or spot the difference between good content and no content at all.