I personally consider it to be cruel and thoughtless to buy an animal without any concern for that animal's needs and health. Don't expect too much at first. Be patient with your iguana and don't misunderstand it's natural fear of you. Stress is a killer. Don't keep your iguana up all night with lights on and music blaring.
Stress causes a weakened immune system and the potenial for illness.
If your iguana is ill, don't wait to take him to the vet until it is too late. If you can't make a commitment to regular veterinary care for your reptile, don't get one. It is cruel to allow a creature to be in pain and to suffer because you don't want to spend the money to take a sick animal to the vet. Many, many are not. The pet industry should be policing itself and eliminating the inaccurate information, inadequate housing, uninformed employees, and, as much as possible, dangerous or useless products.