This behavior being so common is one of the reasons I have a nearly gut-level aversion to services that OFFER a free trial.
I much prefer a free tier of service, with a clear indication of the upsell options. For services I like (like Toggl) that have a free tier of service, I am still skittish of the trials of "pro" tiers, precisely out of the fear that it might be a hassle to cancel, rather than a "we assume you're going to cancel".
Everything I recall reading about setting up a subscription service suggests that the default-to-stay-subscribed method leads to more revenue (as people forget), and as customers we're accustomed to think, "well, that WAS my fault ...". In a normal subscription scenario, even, that probably is nicer to customers. However, for a __trial__, I would prefer to see an end of the paid service, rather than to start receiving bills.
A better example of dark patterns is how they repeatedly try to get you to sync your email contacts by sneaking it in at random points, where you may accidentally click through it.
Their website has also become a minefield of upsell links, some disguised as benign engagement (e.g. "Add a new skill") while others are much more spammy (e.g. "Follow this unrelated business which promotes through us").