However, it's not that difficult to spot if you're paying attention. Two job workers tend to:
1. Have elaborate excuses for why they can't update their LinkedIn profile to show the new job. Obviously they can't tip the old company off that they have a new job.
2. Have mysteriously complicated and ever-changing schedule conflicts throughout the day. We support (and encourage) flexible work, but when someone is disappearing throughout the day and can't reliably jump on a phone call (despite supposedly being online and active) without ample notice, they're probably doing something else.
3. Are extreme people-pleasers in superficial ways (want to keep up appearances) but only actually deliver good work when it's high profile and they know they're in the spotlight.
4. Are loathed by their teammates after a while, because everyone they work with slowly catches on that the person is absent-mindedly doing the bare minimum to not get fired. Inevitably, the teammates have to pick up the slack and do extra work to compensate. Few people are better positioned to recognize this than the people who are in the trenches with the person all day.
5. Have a different jobs on their resume with start and end dates that don't match what you confirm with the company. That's because they need to massage the start/end dates to appear as though they weren't overlapping the two jobs.
6. Are religious about "If I get my work done, why does it matter when I work?" Sounds great, but then they play every game in the book to shrink "their work" to be as small as possible and move the "done" part as far in the future as possible. End result is that team mates suffer (see #4).