I use to work inside a warehouse and I had three incidents when I saw someone who actually wasn't there.
The first time I saw someone I thought it was our boss who was real pain in the butt. The managers inside the warehouse would wear a red vest, he is Caucasian, with blonde hair and blue eyes. I was working in a certain area just minding my own business, and I look over to the left of me where there are just some tables with computers (it is always empty because that area is only used during the day time and I worked overnight). But when I looked over to my left I saw our boss leaning over on the side of a computer and spying on us to see if we were working. I clearly saw his eyes looking at us, his blonde hair and red vest. I just rolled my eyes because I was irritated that he was actually spying on us, it took like 1 second for me to roll my eyes and when I looked back no one was there. It was impossible for anyone to move that fast or hide anywhere else, it was an open space and I can see everything around that area.
It was really weird I thought I was just seeing things until it happened again a long time after.
The second time I saw something like that it was just me and one of my co workers. We went to lunch 30 minutes earlier than everyone else because we wanted to get some work done without any distractions. But when we came back our manager (a different one than before) wanted us to go to the back dock to make sure we didn't get backed up while she was loading packages onto the conveyor, we did not want to because we had our own work to do but we just sucked up and went to the back. There is a board where we hang up our the scanners and right there is where I saw her standing behind, peeking her head out spying on us. She's a short Hispanic lady with dark hair and always has a bun with a hair band in her hair and of course with a red vest. I saw every detail and I even saw her smiling, kind of like a giggle. I turned to my co worker to tell her and when I turned back which was about 2 second later, no one was there, no way anyone could leave that fast and nowhere to be found.
The last time I saw someone when I went to work early to put in some over time, I was the only one there in the back dock cleaning up. Then I saw a girl walk out of a trailer where we load packages (wearing an orange vest so this person really stood out, we all have to wear some type of vest for safety and visibility), she was walking towards the ship clerk desk that was just left of where I was standing. I walked the same way as her and I saw her walking passing the poles and big cardboard boxes (the only time I did not see her was as she was behind the cardboard boxes passing them), and once I got to the ship clerk desk I did not see her anymore, she was not anywhere in sight, it was weird but then again I was use to seeing things like that at work by this point. I did not get and bad energy from these experiences, I wonder if anything has happened in that area.