It can be difficult to accurately determine whether a mushroom is poisonous or not, since there are many different types of mushrooms, and some poisonous species may closely resemble edible ones. However, there are a few general guidelines you can follow to determine if a mushroom is poisonous:

1. Look for warning signs: Some poisonous mushrooms have distinctive characteristics that will help you identify them as toxic. These include bright colors, an unpleasant odor, or a slimy texture.

2. Check the mushroom's habitat. Some poisonous mushrooms only grow in certain environments, so knowing where the mushroom was found will help you determine if it is toxic.

3. Consult your field guide. There are many field guides available to help you identify different types of mushrooms. Look for one that is specific to your region, as mushroom types may vary by location.

4. Consider the characteristics of the mushroom: Look at the cap, gills, stalk, and overall shape of the mushroom to identify it. Note any distinctive features that may indicate whether it is poisonous or not.

5. When in doubt, don't eat it. If you are unsure whether a mushroom is poisonous or not, it is best to err on the side of caution and avoid eating it. When it comes to wild mushrooms, it's always better to be safe than sorry.

Remember that unless you have experience identifying mushrooms, it is best to consult a specialist or experienced forager before consuming any wild mushrooms.