My first A&A experience was a bit underwhelming, but partially due to the product I bought. The Firepower F4 carbine (yeah, piece of crap) essentially fired 10 rounds before the mechbox blew apart. And the KJW M9 shipped with a broken mag. But Mark accepted it back (at his expense for shipping) and we made arrangements to upgrade to the CA M15A4 instead. I had that and the new M9 mag in a few days.
So in the end, he made things right in a timely manner, and what more can you ask from a retailer? They'll get more of my business in the future for sure.