Look at the thickness of the wrought iron. The thicker the wrought iron, the better. It gives durability to the furniture.
Check if there is extensive damage to iron. Such areas are prone to rust. Small rusty areas can easily be cleaned using sandpaper, and then the area can be repainted.
Look for a powder coat to protect against rust and provides weather resistance.
Consider buying the set with cushions. Those that come with a set typically fit best. Ensure they are waterproof.
Try folding models if you entertain frequently and need to move the furniture around your patio or yard. Do test folds to ensure they fold easily.