Corals can be very forgiving animals and oftentimes the following tend to be the main factors in shipping them: the care taken in handling and packing them, shipping weather, and the type of coral being shipped. If packaged correctly the majority of common corals purchased have high survivability, but ime sps
corals have the added protection of a hard calcareous skeleton, which provides some cushion while in the bag. LPS
and soft corals do rather well if suspended by styrofoam to allow oxygenation and keep from settling where tissue can be damaged and/or just rot. Many palythoas, zoanthids, mushrooms, and gorgonians do quite well just sitting at the bottom of a well-prepared bag.
Once you receive the corals make sure to check temperature, pH, and salinity so you can determine what type of acclimation is needed, if necessary. When I acclimate I prefer to float the bags for 10-15mins for temperature equalization and an hour flow-through drip; however, if the bag looks tinted (usually brown due to coral "stress") I will assess the corals health and either give a fast (non-restricted) flow-through drip or place the coral immediately into quarantine or its display. Sometimes you receive stock in very poor condition and judgment calls must be made, but this is where their resilience can surprise you. If any other questions feel free to ask