A specimen will most likely calm down with interaction, but a calm specimen is a much more enjoyable pet. Hunger folds are another sign of malnutrition. Although it is generally not a problem with Red Tails, check to see if the specimen is a known feeder. Ask to be allowed to watch the next time it is fed, maybe even offering to purchase the food. However, I would wait at least 1-2 days before moving a just fed Boa.
Mites are no reason to reject a snake, but are definitely something to look out for.
I have seen neonates ranging from 12 to 24 inches. Growth in newborns is very rapid, between 3-5 feet in one year. The second year can yield lengths of 4 to 7 feet. Adults range anywhere from 5 to 10 feet, with an occasional 12 and 15 footer thrown in just to keep us all on our toes. Growth is directly related to diet and housing conditions.