Actually if you hire installer to install the camera, ask them to do free 6 months free matainance,if they are happy to do it that means the system real reliable, if they just ask you to buy cams and he just install , all warranty will just ask the supplier will be careful about the quality. You know install a camera is much easier to maintain a cam.
This also suit the installers, recommend a reliable system is much better than just earn 10-20usd on each cam. Because you will cost 100-200usd to maintain it.