Former investigator here. Have performed and managed literally thousands of background checks.

1)

Employment verification is part of the standard background check but so is establishing online profile. But it’s usually valueless: if you don’t have a letter of recommendation from an old boss, most companies’ policy is to say “yes, Alex Rodriguez worker here from May 2000 to June 2004″, and that’s it. You rarely get any useful information from reference checks.

2) Very few HR depts actually know how to conduct a proper background check, usually it’s outsourced. Background checks are usually only done after an offer is made. How intensive the check is will depend on how much money you want to pay, which depends on how important the candidate is, what the industry is, and how organized the HR dept is.

3) A proper background check goes more intensively into online profile than just google. What we’re talking about here is just HR people and managers idly googling you. If they can do it and find out you look like a douche, then clients can do it just as easily. How much this matters depends on how important you are or how much your firm wants to hire/fire you.

Bottom line: the internet is a public space open to all. Don’t make any comment in your own name (or traceable to you by image, email address, phone number etc) that you wouldn’t want printed out and posted on the noticeboard at work. And never trust social networks’ privacy settings!