ABA can be a kind of debatable topic to say the least -
With any behavioral therapy, it is important to remember that not everything can be solved behaviorally, some problems just exist for purely organic reasons and may not be remedied with anything but time for maturity.
Another thing to think about is what kind of modification... is the therapy to replace undesireable behavior with an acceptable behavior, to extinguish a behavior, or to initiate a behavior?
In each case, you have to seperate each behavior you are working on and assure that the 'replacement' type does not initiate a behavior that might be unnaceptable in a year or two, or the 'extinction' therapy does not produce a 'dead man' effect, etc.
And last, any rewards should have careful consideration, I know that food rewards are high on the list of what causes debate on this.