1. Before opening the bottle, if you find that the cork is protruding from the bottle, it means the wine may have been exposed to high temperatures, causing the pressure inside the bottle to rise and push the cork out.
2. If a red wine's color is dull, lacks luster, or appears brownish, it may have been over-oxidized or contaminated by other factors. Similarly, if a white wine shows a very deep yellow color, it may also have undergone excessive oxidation.
3. If you find bubbles in a still (non-sparkling) wine, it means the wine has likely undergone a secondary fermentation in the bottle. However, not all secondary fermentations are signs of spoilage; some wines are specifically handled by the winemaker to continue fermenting after bottling, such as Vinho Verde from Portugal.