Avocados are best ripened at home so you can use them just as they become soft. It can be risky to buy ones that you think are already ready at the store for two reasons.
Firstly, you don’t know how long it has been soft for. From my experience, there’s a fair chance it will be overripe and starting to go off in the middle.
Secondly, if a loose avocado has been sitting on the supermarket shelf for long enough to turn ripe it may have had a lot of fingers pressing into it and bruising the pulp.