Carefully study this: Cliff Notes.
Andy provides 2 yr warranty. And has stepped up for those here that had problems.
If you want "support" (not sure that really exists anywhere anymore) then you can purchase from B&H Photo., at a much higher cost most times.
Beware, some of the better cameras that we talk about here, never make it to the US Market, thus not available from B&H.
There have been firmware issues with some of the newer cams, that Andy has been able to provide feedback to Dahua given by us, and get the bugs worked out. Then supplies the improved firmware here. Not sure how much better support you need.
The camera's he sells has shown a very very small minuet failure rate. Most of the returns he gets is from user error, nothing wrong with the camera.
Amcrest are OEM'd by Dahua, with features sometimes removed.