Even if a plant is blooming when you buy it, be patient with it. The shock of going from a garden center to the typical home may cause an orchid to skip a season before it performs again. Don't get frustrated and throw it out, and don't take it personally. It's worth the wait.
Leaves — The same principles apply as when buying any plant. Look for medium-green, uniformly shaped and colored leaves with no black spots or streaks.
Insects — Greenhouse-grown plants are more susceptible to insects than home-grown ones. Don't buy infested plants — why take home trouble?
Roots — Look for white, fat roots with healthy green tips poking through the potting medium.