In some areas, the eggs are sliced out of the female, the female crudely sewn back up and let go, the assumption being that she will survive to lay again. There the iguanas are dumped into other bins, generally with the dead and dying not sorted out. If they are lucky, some form of food and water is thrown in with them. They are then grabbed and stuffed in shipping containers to be sent to pet stores. But captive bred iguanas are tamer than wild or farmed ones.
Iguanas are a lot like dogs, people and other living things.
Some are just naturally nice and others mean. On the whole, however, 'nasty' pet store iguanas are those who still have the strength to fight back, while the 'tame' ones are merely too sick to do so. Animal protein makes my iguana nasty. There have been folks who have reported that their iguanas get aggressive when fed animal protein. It may merely be that they were fed inadequate plant proteins previously.