The first one I owned was a jersey wrap dress from a supermarket clothing rail, bought in a rush for a wedding I had three days to prepare for. It taught me that a wrap dress in cheap jersey stretches out at the tie within a month and never quite snaps back, so by the second wear the whole thing sits an inch lower than it should.
Plus size dresses as a category cover such different jobs that it's worth being honest about where they fall short. A rigid cotton shirt dress, the kind with a stiff collar and structured bodice, can look brilliant on a smaller frame and turn into a box on a bigger one if the brand has simply graded the pattern up rather than rethinking the shaping around the bust and hips. Bodycon in anything without real stretch will show every seam line and every bit of static cling, and if you're sitting at a desk or in a car for long stretches, a dress with no give at the waist will remind you of that fact every twenty minutes. Anything with a fitted waistband and no side seam allowance is also a bad idea if your measurements shift through the month, because there's no room to breathe into it.
Before I buy now, I check three things on the product page that tell me more than the photos do. First, the fabric content, because a dress that's mostly viscose with a touch of elastane behaves completely differently to one that's polyester through and through, the viscose drapes and breathes, the polyester clings in summer and holds smell. Second, where the zip sits and how long it is, because a side zip that only runs to the hip on a fitted dress means getting it on is a two person job, while one that runs further gives you room to actually move your arms getting it over your head. Third, the lining, particularly on anything in a thinner fabric, since an unlined dress in a pale colour in direct light becomes a different dress entirely. The ones that disappoint are usually let down by flat, unfinished seams that start to fray after two washes, buttons that are glued rather than properly sewn through, and hems that were clearly cut straight across a pattern without accounting for how the fabric falls differently over curves. A well made one has a bit of weight to the fabric, proper flat felled or French seams, and darts placed where your body actually changes shape rather than where the pattern assumes it does.
If a dress has a defined waist, try sitting down in the fitting room before you decide, not just standing in front of the mirror.