The first thing I do with a relaxed hoodie is pull the body fabric between my fingers and see what happens. A proper loopback cotton has a bit of weight and bounce to it, it springs back. A thin cotton poly blend just stays flattened, like it's already given up before you've worn it once. That one test tells me more than any label does.
A relaxed hoodie doesn't play well with anything else that's also trying to be the loose, slouchy piece in the outfit. Wide leg joggers underneath it and you've just made a sleeping bag with arms. It wants something with a line to it, a straight leg jean, a slim trouser, anything that gives the eye one fixed point so the whole look doesn't read as "got dressed in the dark". It also clashes with structure up top, so don't layer it under a fitted jacket and expect the jacket to sit properly, the shoulder seam will be fighting a battle it can't win.
What separates the ones worth keeping from the ones that end up as a cleaning cloth is mostly in the details you don't notice until you've worn it eight times. The ribbing at the cuff and hem should hold its shape and bounce back after a stretch, not go slack and flappy by week two. Flatlock seams lie flat against the skin rather than digging in, which matters more than people think once you're sat down for hours. The drawstring should have proper metal or moulded tips, not a bit of frayed cotton that disappears into the hood the first time you yank it. And the hood itself should have enough body to stand up a bit at the back rather than collapsing into a sad little flap.
Where it falls short is anywhere you need to look pulled together on purpose. It is not an office piece, not even a casual Friday one, no matter how good the fabric is. It won't do you any favours under anything fitted, and if you're already a fuller build through the middle, going bigger in the hoodie just adds volume in the wrong place rather than hiding anything. It's also not the one to reach for if you're standing for a long day, the fabric that makes it soft is usually the same fabric that goes limp and clingy by the afternoon. Know what it's for and it earns its spot. Ask it to do a job it was never built for and you'll just end up disappointed in it, which isn't really its fault.
The one mistake, and I see it constantly, is sizing up when the cut is already generous. Check the actual body length and shoulder drop before you add a size, or you'll end up wearing something that looks borrowed from someone twice your height.