If it's a slabbed book and from GPA/GoCollect/eBay you know that the FMV ~300$ then I can understand why as a potential buyer you are displeased.
But if it is a raw book I will generally prefer to buy here than in eBay.
I once bought a raw book graded as 9.0 from eBay. 8 months down the line when I wanted to sell it via Mycomicshop, their grade for the comic was 6.5 -- due to a flaw that I had missed altogether.
In contrast, few months back I bought a book as a raw 7.0 from a boardie, that when I sold, was eventually graded as 7.5 by Mycomicshop.
Although I have cherry picked extreme examples, I am more confident buying a potentially correctly graded raw book from a boardie here maybe even at a premium over FMV than on eBay.