I think that at big box stores, the trick is to get them at the right time.
Not too early because they stock some things way too early for planting, then when the time is right, get there and buy the freshly stocked good looking ones before they ruin them. When they have those end of season sales, have the critical eye to spot the healthy plants and don't get lured into buying sale plants on their "last legs" unless you are sure of their survivability.