Here are a few things to look for to help reduce the likelihood of being disappointed when you cut open your avocado.   The firmness of the avocado should be dictated by when you plan to use it.  If you are buying it on the same day you plan to use it, it should slightly give in pressure when squeezed but not be overly soft.  If you plan to use it in a few days, choose a firmer avocado.   Check the stem end of the avocado.  It should be slightly green and not overly brown. If part of the stem is still there it should easily come off. Avoid avocados that are shriveled, have spots or are super soft when squeezed. Avocados that are bright green and hard may have difficulty ripening properly and are best avoided.