Last summer I co-oped at a company in the DC area. Company was a contracting company that did construction in the DMV area. I made mistakes from the beginning when I got this job.

When I went to the career fair, I only chose positions in the DMV area. I had a LDR with a guy from Richmond, and I wanted to be closer. My university isn't close to this. Lesson 1: avoid constraining your location preference if possible.

I snagged an interview with these guys. My GPA was shitty, it was spring of my sophomore year, and I was desperate because everyone else was getting a co-op and I wasn't. I think I only joined the co-op program "because that's what everyone does". I got the job without asking very many questions about what I'd do. Lesson 2, 3, 4: avoid peer pressure. Be patient. Ask questions in interviews!!

I was given a $700.00 stipend per month to find housing. I took that as a $700.00 maximum on my rent because fuck paying rent with my own money. I found a woman renting out her spare bedroom 7 miles away for 700, and 2 college kids looking to sublet a room 12 miles away for 800. I googled the woman and found awful things about her, including financial troubles with a restaurant, her shitty treatment of customers for her laser hair removal services, etc. On the phone, she mentioned that her landlord doesn't pay attention (read: her landlord won't know about me) and that she has a "friend who comes over to use the computer in the spare room sometimes". This "friend" was her 15 year old son and he stays in the room on weekends because there are 2 single beds, something she didn't mention over the phone. I elected to stay with her (because money and distance) and drove 160 miles away to my SO's on weekends so I wouldn't have to share a room with her underage son. Lesson 5: Don't be cheap about housing.

The co-op was shitty. Literally. Here is a comment I made last summer describing it:

I work at a sewage pump station. We are rebuilding the site currently, so we use these sewage bypass pumps to push the wastewater to the next station.
However, these bypass pumps aren't perfect, and get clogged. Toilet paper, shit, clothes, plastic, etc builds up and you must unclog it.
That is where my job comes in. I am an intern. I signed up for a project management co-op position. Not a fucking shit raker. One of my jobs is to turn off the pumps, let the pressure out, unhook the giant, heavy tubes (pictured above), and pull the clog out at least once a day.
Yesterday, the clog in pump 1, the primary bypass, was abnormally large. I was checking the pumps before I left the site (6pm). Now, everyone is getting home around this time and using the bathrooms, so the pumps are working hard. Anyway.
I turn off pump 1, wait for the pressure to go down, and unhook the tube. I slowly pull out the gigantic shitmass of toilet paper, feces, and god knows what else. As soon as I pull the last bit out with a satisfying "thwop", the backed up wastewater shoots out at me. I got covered in it.
I threw up. I wanted to light myself on fire. The lukewarm shitwater soaked my jeans. I quickly reconnected the tube and ran to the trailer, where I soaked myself in hand sanitizer and ripped off my jeans. Thank god I took the advice of my supervisor and had a spare pair with me.

This, plus having no plumbing on site 3-5 days a week, getting a call from the pumps at 2am (they are automated) because they are clogged and to perform what I said above, plus my boss being a total dick, are why it was shitty. Problem is, I never did anything about it. I never said anything to my co-op office. I never said anything to my boss or the people who hired me. I never quit. I cried every day. I became depressed.
Lesson 6: Respect yourself.

tl;dr shitty co-ops are shitty. I am a completely different person because of this co-op. I went through a horrible experience, sacrificed my self respect, my dignity, and a whole summer because I felt it was necessary. Do not ignore the red flags. If you feel uneasy about a co-op, do what is best for yourself professionally and personally. There is no shame in not getting a co-op your sophomore year. There is nothing wrong with doing internships instead of co-op - do not feel obligated to do one or the other. Trust your gut.