Hairlines

New to the forum, but glad to be here :-)

I recently won a "lot" of 20 Peace dollars on ebay that included a 1928 gem. Got all 20 for $559. The 1928 looked to be in really outstanding condition, even mint state. So I knew I got a deal.
When the coins arrived, the '28 was absolutely BEAUTIFUL! It had that light gold tone with full luster, cartwheel, and eye appeal. I was floored.
So I took it to a coin dealer and he put it under some kind of really bright light and immediately declared that "I wouldn't get this graded, it has hairlines".
So I took a look, and, sure enough, I could see a very light indication that at some point, the coin had been, perhaps lightly brushed or rubbed, maybe even cleaned. With the naked eye in normal light, this is not noticeable. Needless to say, I was a bit distraught. How could a coin with such absolute beauty now be ungradeable?
Here's the auction: http://www.ebay.com/itm/121863109981
If you look at the picture of the reverse, you'll see that the hairlines are clearly there. Being the novice that I am, I missed that aspect, because I wasn't looking for it.

Just how much do "hairlines" affect the value or condition?
I know it's a grey area, because not all hairlines are created equal, but hopefully someone can steer me in the right direction, and maybe even point me to some good reading on the subject.

On a similar note, I see that on many many auctions, people are bidding big dollars (relative to the coin value) on far worse examples than mine.

Thanks for taking the time to read this, and hopefully set me on a straight course :-)