After reading it all(trying to keep phone time wile at work interesting and usually missing half the thread which i shouldnt do......) i would like to add two things about this SG.
They are pretty rare, at least i cant find many, PLUS a good SG is very very rare especially among the low priced issues. Usually good gibsons are picked by good players who also often play it live, so there you go, the big tonemonsters are usually not the lookers.
What wil tell you alot about the quality of your SG is doing a couple of harmonic sweeps high up the neck, a good SG will chime, start to sing(or scream when using overdrive) without much effort, think Iommi here youll know what i mean. If it sound dead as a board its not a good SG IMVHO, if it is your damn lucky. Mahagony, if it is the good kind of tonewood and is made well has a very abundant high pitch harmonic, or sparkle if you want, youll notice it when you try the above(is mahagony exclusive IMO), at least i do. You can also hold the end of a tuning fork against the body(or just tap it) but that will take alot of experience to hear all the nuances i think. Maybe someone experienced in your neighbourhood can help you out if you dont feel convident judging a guitar that is offcourse.
And yes if you look at the price they did cost originally you payed way too much, im actually quite sad about this since i could have told you this before you bought it, then again you probably know that yourself and thats why you are unhappy with the looks of it.
If i were you i would try and get the seller to take it back IF the SG is a dead sounding plank, or put it on the bay again after giving a correct feedback to the seller and take the loss like a man, youll be laughing at this if you knew the losses i had, if put in perspective so......
So thats what i think, being truthfull as hell again and i hope i dont offend too many people around. I always feel i am really blunt about things compared to you nice english people, over here its rather the opposite strangely enough......
Anyway, hope this helps and you wont be offended by my blunt way of putting things.
Best of luck, Henk