Recruiters paying to have premium access to candidates (a large part of LinkedIn's revenue) does not appear to involve tricking anyone.

Indeed many people joined LinkedIn specifically so that prospective employers could find them.

Their shadiness is not limited to usability dark patterns; I am fairly sure they're scraping people's contact lists from gmail and the like without consent via impersonation (have gmail open in one tab, linkedin in another...). Exactly how they're accomplishing that, I'd love to know -- Facebook is likely pulling the same trick.

That's a pretty wild claim; what observations have led you to this conclusion?

Hi have noticed this repeatedly as well. Under the "People you may know" section, I see names of people with whom I've emailed only 1 time, often many years ago. These are people with whom I have no relationship, and the only record of them in my life is a gmail email. This leads me to believe that LinkedIn is somehow accessing this data without my permission.

Actually, that makes perfect sense, with no need for exotic cross-tab scripting attacks.

That person may be in your address book, which you've never shared with LinkedIn, but you are in their address book, which they clearly have shared.

Plausible for some, not others. I've seen LinkedIn suggest I connect to "people" that aren't people at all, but role addresses. E.g., reception@[my oral surgeon]. Others are email addresses that are ancient, 15 years old at least, or for domains that no longer exist.

No idea how they've gotten access to that, but I've never knowingly authorized a connection to my address books.

This is the behavior I have observed too. There are addresses that could not plausibly be gotten by any means other than unauthorized scraping of my mail or contacts.

The only other mechanism I can think of is that maybe they're getting them via Android or iPhone apps (not necessarily linkedin's app) with less-than-upfront disclosure of what the app's doing. Either way, it's slimy behavior.

Wouldn't it be possible for LinkedIn to infer that you might have a relationship with a person based on that person's relationships with other people LI knows that you know (or even overlap of companies, city/industry pairs, etc.)?

LinkedIn bought Rapportive....

Rapportive captures the contact info of every person whose email you open (or who you write to).

What's more likely is that people that you contact via email are allowing LinkedIn to search their contact list.

Linkedin makes Facebook look like a real good deal.

At least Facebook has cat pictures and games.

what sort of things do they do?

This is a serious question, I don't know and am curious.

The most provable thing is that if you ever make the mistake of granting them access to your email account, everyone on your contact list can expect multiple spam messages FROM YOU begging them to join LinkedIn. It's the kind of thing only the shadiest of shady Facebook apps employ.

Harvesting of contact information even without permitted access is less clear cut but there's widespread concern due to the large number of questionable coincidences.