Size and plumpness: Larger birds are older and therefore more muscular (and flavorful). A round, plump chicken is usually a juicy one. If the skin is shriveled and looks dry, the meat probably is, too.
High turnover: Are the chickens prepared and replaced daily? Ask the person behind the counter to make sure.
Color: A well-roasted chicken should be golden brown. If it's too dark―more mahogany than birch―it may have been in the oven too long and is probably dry. For the same reason, avoid chickens with wing tips that are scorched or burned.
Clean packaging: Take a look at the other store-prepared foods. If everything looks clean, it's a good indication that the store adheres to sanitary practices.
Heat: If you're buying a rotisserie chicken, the rotisserie should be providing steady heat to guard against spoilage. (If you're not going to eat the chicken within two hours, refrigerate it. It's safe there for up to three days.)
Organic or free range: Organic, free-range chicken will always taste more like you made it at home