Buying a hail damaged car is something that should be done very carefully and with a lot of research. Anyone selling a damaged vehicle has a vested interest in underselling the severity and cost of any repairs.
Pictures can be used to help guage the level of damage but they are often a poor guide - dents do not show up in photographs very well. Every dent is different and needs to assessed based on size, placement and access. If panels need to painted or replaced this can add significant time and costs to the repairs.