Hi
Overall Marantz built quality is quite good and HDMI boards getting burnt is a common issue in all brands due to various factors like Electric current being passed through HDMI which comes from set top box (Cable TV) or either the electric outlet where the AVR is connected is not in proper order and hence causes short circuit etc.
There are a lot of dealers / sellers who sell the proper AVR or even refurbished products. You need to be cautious and check if you are purchasing from a proper authorised dealer who provide warranty. You can pick the AVR from HifiMart or other known dealers who provide a good rate.
All the best!