This is the single most common disappointment in online clothes shopping, and it has two separate causes that need two separate checks.
The first is appearance. A garment photographed on a 180 cm model reads completely differently on a different body, and product photos are styled, pinned, and lit to flatter. Virtual try-on addresses this directly by rendering the item onto a photo of you, so you can see where the hem actually lands, whether the colour works against your skin tone, and whether the silhouette suits your proportions.
The second is fit, and no visual tool solves it. For that, find a garment you already own that fits the way you want, lay it flat, and measure the chest, waist, hem, shoulder seam to shoulder seam, and sleeve or inseam. Compare those numbers to the product's flat measurements, which most quality retailers publish. If a site only lists body measurements, add roughly 5 to 10 cm of ease for a relaxed fit and 2 to 5 cm for a slim one.
Two more habits close most of the remaining gap. Read the fabric composition rather than the marketing copy, since "100% cotton" and "95% viscose with elastane" behave completely differently once worn. And search the reviews for words like "petite", "tall", or "runs small" rather than reading the star rating, because sizing consensus in reviews is usually more accurate than the brand's own chart.