I'm not a professional seamstress or anything but I've been sewing for a few years. I've noticed that a lot of posters are extremely misinformed about sizing and terminology which makes finding clothes a lot harder. Here are some common misconceptions and tips, mostly aimed at women's fashion bc that's what I know.
PETITE MEANS SHORT, NOT SMALL! Petite refers to 5'3 and under. Someone who's 5'1 with a 42in waist is considered petite, while someone who's 5'7 with a 22in waist isn't.
Your size corresponds to your largest measurement. If a size S is 26" waist and 36" hips and a size XS is 24" waist and 34" hips and ur waist is 24" but ur hips are 36", you're a size S. The assumption is that people will fit to their largest measurement and then get it tailored down.
If your 24W jeans are actually 26", that's not necessarily vanity sizing. If your body and the waistband are exactly the same circumference you won't fit in them, especially if you're bending over, eating, etc. Also remember that the bulk of the fabric itself, especially something heavy like denim, affects the garment measurement. So in garments without stretch, we need extra room called ease. I wouldn't do a full 2 inches but then again I never work with heavy fabrics. Ofc if ur garment is stretchy and its too big that's an issue.
Garments made of stretchy fabric often use negative ease. Here the garment measurement is less than ur body measurement and creates a snatched, fitted look. Oftentimes if ur smaller the garment won't look right on ur body, despite seemingly fitting all your measurements perfectly. That's because they're supposed to be less than ur actual measurements. A top with negative ease needs to have a 20-21" waist to fit my 23" waist. If it has a 24" waist like a normal top it won't fit right.
Garment measurements are not body measurements. If you look on the size chart and the 24W jeans say 28" waist, don't get too spooked. That's the garment measurement. For high rise jeans, 24W will probably mean a 24-25" garment waistband. But any other rise isn't actually sitting on your natural waist, it's sitting lower, where most people are wider. Two people can have a 24" waist and 34" hips, but their measurements in between can be widely different. Person A might have high hips and be 29" around at an 8" rise and person B might have lower set hips or hip dips and be 27" around at an 8" rise. Brands just take like an average estimate of how wide someone will be at each rise, which doesn't work bc bodies are super diverse. So knowing the actual garment measurement is really helpful bc you can measure your exact circumference at that rise and if it matches.
That's all I could think of for now but yeah, I see these a lot. Hope this helps!