Many of our members (included myself) have purchased from them and the Denon receiver that I got from them looked and performed like new.
Both Onkyo and Denon are popular with our members. I have had Denon gear for many years and it has been very reliable. Some of the Onkyo receivers have heavier power supplies, which tend to produce more continuous power. However, there have been a few reliability problems in the past, which I am sure that have been worked out now.
As long as you stay with a brand name you should be fine. Marantz and Yamaha have also been popular with our members.