When you feel like it's an easy one for once, it might be so but you'll still flunk it if you think so.

A friend will tell you "ok you're about to date a serial murderer, I strongly suggest you reconsider but if you don't that's fine, it's your choice." A manipulator will tell you "NO YOU CANT SPEND TIME WITH THEM THEY LOOKED AT YOU FUNNY I FORBID YOU FROM BEING WITH THEM!!"

Your situation is going to be between those extremes: it's going to be more of one than the other, and you'll know which.

In no particular order:

Advice is usually worth (at most) what you pay for it.

The harshest lessons are about trusting the wrong person.

No one will have more words for you, than a lazy person who wants you to do something for them.

Judge weak people by their natures, and strong ones by their goals.

If possible, don't be poor. If you are though, be wary of following advice on this topic from people who have never been poor for an extended period.

I really disagree with your secondhand comment. Buy more secondhand, less new! Cheaper, better for the environment, and you can find some cool things you wouldn't otherwise. I get nearly all my small kitchen appliances from thrift stores. Most people get them as like a wedding gift or something and then never use them, so they are practically new. All my clothes except underwear and socks are thrifted, most of my furniture, my dishes, most electronics... I love thrift stores.