Are there any PC parts at all that could get damaged by anything less than sitting unboxed in direct sunlight on an asphalt road in 50°C weather?
I'm really asking... because otherwise, I can't think of anything that would get hot enough to fail from sitting in the heat... HDDs, maybe? (I don't know what safe temps are for those.) Maybe an unpackaged pre-built with a black metal case in direct sunlight?
It gets up to 45°C where I live, and I store PC parts in my almost-as-hot garage all summer long. Never had a problem from doing this, and never even worried about it.
Salesperson is full of crap.
As for Newegg... I've been hearing horror stories about their customer service for 15 years. I try to shop elsewhere if possible, but when I do, I personally haven't had a problem yet. Their use of mail-in-rebates really sucks, though. Don't be swayed by mail-in-rebates.