If you are in Davao City where durians abound, the cart seller will choose for you, you only pay if the durian is good, if it is not good enough, he changes it with a good one.
In metro manila, in my regular fruit stand, I ask them for a guarantee like above.
Otherwise in the wholesalers, I will just have to take a leap of faith that it may be good or not so good.
If you are to ripen them yourself, you can knock them with your knife, it goes thud... it's not yet ripe, if it seems hollow, than it is ripening.
There's also smells and cracks when ripe and the stem on top lopping off may signal if it is ripe.
Unfortunately some sellers may have picked the durian too early and it's not so good.
Your mileage may vary.
