Well, some thoughts:
Sprague Atoms - newer ones aren't that great, but the ones in the amp were made in the latter 80's, does this change your view? The new issue Mallory quad cap is pretty much junk and won't last very long (it will pop and sizzle and might even spew out). The rest of the components are average, nothing more.
Gold plating and silk screening - having had some ST-70 chassis chrome plated over the years, I seriously doubt you get that done for anywhere near $400... likely more than double that. EPA regulations make it very expensive to do this kind of work nowadays.
Tubes/Sockets - sockets look cheap... tubes are nothing special and one of the output tubes has a broken locating stem. Also the rectifier doesn't look to be lit, so either it could be bad or the transformer winding is open, hence the SS rectifiers.
Overall, nothing special in any way, sans the chassis work which does look nice in the pics. It's also showing free shipping. Ebay is nothing but a service... if the guy put it in the local newspaper classifieds, would you now hate your local newspaper? The world is full of greedy people, always has been, they have access to the same tools and services as everyone else. Do some homework first, then avoid the low class people that are simply looking to rip-off the general public. Dare someone actually say, "buyer beware"?
Regards, KM