The first thing I do with a zip hoodie is run the zip up and down twice before I even look at the price. If it catches on the fabric at the bottom or feels gritty going up, that is how it behaves forever, not just in the shop. A good zip glides with almost no resistance and has a bit of weight to the pull, something you can grab with cold fingers or half asleep, not a thin little tab that snaps off by March.
Past that, it is about what the zip is attached to. Thinner hoodies with a flimsy zip sewn into stretchy cotton will pucker along the seam within a few washes, so the front goes slightly wavy and never sits flat again. Look for a tape that is stitched down properly on both sides, not just caught in a single line of thread, and a fabric with enough body that it does not pull away from the zip when you move. The inside tells you more than the outside. A brushed, slightly fluffy lining that still feels soft after a wash is the sign of a decent one. If the inside feels thin and slightly plasticky even new, it will go bobbly and flat fast. Metal zips tend to outlast plastic ones, but only if the fabric around them is substantial enough to hold them without fraying, so check both together rather than judging the hardware on its own.
Colour wise, I have learned to stop buying anything too pale if it is getting proper wear, because the zip area and cuffs show grime first and a light grey or white hoodie front looks grubby long before the rest does. A mid grey, a soft navy or a plain black hides that and still looks easy with almost everything, jeans, leggings, a skirt even, which I did not expect the first time I tried it. Bright colours are lovely for a season but they fade unevenly round a zip, so I keep those for the ones I am not relying on long term.
If someone has none of these at all, I would start with a mid grey or navy one in a slightly heavier fabric than feels necessary in the shop, because it will stretch and soften with wear rather than thin out. Skip the oversized novelty prints for the first one and get the plain, well made version, it will get worn more than any of the fun ones.
So before I buy, I ask myself one thing: if I run this zip up and down fifty times this month, not once, is it still going to feel this easy?