The idea that settlement-free peering always assumes symmetric flows is a common myth. Nobody expects peering with a residential ISP to have symmetric traffic because that doesn't make sense, of course the flows are going to be overwhelmingly towards the residential side of the link.
Back in 2014 when all this was going on Level 3 published an unusually scathing series of blog posts where they called out residential ISPs for deliberately allowing their exchange links to saturate in order to extort extra payments from Level 3 and their customers.
Back in 2014 when all this was going on Level 3 published an unusually scathing series of blog posts where they called out residential ISPs for deliberately allowing their exchange links to saturate in order to extort extra payments from Level 3 and their customers.
http://web.archive.org/web/20140512082831/http://blog.level3... http://web.archive.org/web/20140512082813/http://blog.level3... http://web.archive.org/web/20150508143932/http://blog.level3... http://web.archive.org/web/20150313121250/http://blog.level3... http://web.archive.org/web/20150320123512/http://blog.level3...