Disagree, any manipulation to a suspension is going to change the way any vehicle handles and how smooth or unsmooth the ride is. The customer needs to take some responsibilty for the situation as well. You can't rely and expect everyone to inform you of every detail-you need to educate yourself for your own safety.
it's a matter of good customer service.
and as a newb, going to a professional tech, they SHOULD definitely have told him that lowering the bike can adversely affect ground clearance and handling. As people say "ask the experts". If they're going to do the work, they have a responsibility to inform him of any likely possible adverse consequences. this happens in all aspects of today's society, from full disclosure in repair work orders, buying a house, getting a mortgage, having treatments/surgery by a specialist, taking medications, etc., etc. Our society demands and expects full disclosure. I don't see how a motorcycle shop/store (and a major one at that) should be exempt in any way.
When i had my bike lowered by Z1, he went out of his way to discourage me from doing it, for the way it would affect my handling, etc. I insisted, and the work was done, but i was fully informed. Had anything bad happened, I would completely be 100% responsible.
for the tech's at kahuna, they SHOULD have known that lowering the bike 2" would likely cause bottoming out and should have told him at least that much. I've been riding for 8 years and have had 4 bikes and would have believed the tech as well if they told me lowering it 2" would not be a problem.
Also, there is a proper way to lower a bike (adjusting springs, dampers as needed, etc) and a wrong way (only slapping on lowering links and nothing else). This should have been disclosed to the customer as well.
Instead they just said "yeah, no problem"...this was a new bike sale too, to a new rider. it's not like he rode the bike around and had an opportunity to get a feel for what it was supposed to feel like, or had a chance to research the topic in depth, or had any real experience to draw upon.
He asked all he needed to: "will it be okay? can this be done?"
The advice the shop gave him was poor ("yeah, no problem"), and perhaps (i'm speculating here) motivated to finalize a bike sale. as such, i believe Kahuna should be liable. if not legally or morally, than for the sake of just good, agreeable customer service -- the lack of which is what the OP is really complaining about.
Just my 2 cents