If a deal looks too good to be true, it usually has some kind of catch. Reading comments with real body photos is one of the best ways to check sizing. I also started paying attention to how websites display sizing charts for clothing.
When every picture has different colors or extreme filters, it is usually a bad sign. Online shops that show detailed measurements and care instructions usually get my attention. If buyers say the item runs small or large, I always adjust my choice accordingly. A simple pair of glasses or a basic jacket that always works is worth a lot. Footwear is even harder because different brands cut shoes very differently. Sometimes a store looks great in ads but the real product is completely different.