Even the most "trustworthy" site is going to have spam and scams, just a natural part of the Internet. I was required to use LinkedIn for my college degree, but now I'm scared to see what my message box looks like as I don't bother checking it (think its been a year or more now). Though I doubt I have anything major as my footprint on that site is insignificant due to not building contacts or networks. Think all my contacts are just employees and graduates from DeVry University.
I checked to see if I got any spam or scam messages or questionable contact requests, but had nothing of interest. A LinkedIn message trying to get me to use Premium and three contact requests, all DeVry grads. Did find out that a contact, five months ago, endorsed me for video games as a skill.
As long as you can spot spam and scams you are safe. Had too many acquaintances fall for scams, a former nurse that came to our house had lost $100 because she fell for an email claiming she had to reset her password, not realizing that the site didn't charge to reset the password [as most sites don't]. My sister-in-law's relative lost thousands because she received a call claiming my her and my brother-in-law were in prison in some country and it was needed for their bond. It was after the fact that she found out they never travel outside the US. So, again, at least you can spot the scam before it is too late.