Should I return this laptop? Ebay purchase. Please help - need more than one opinion! College student here

Question

First, it was an amazing deal of $525 for a 2011, 6gb RAM, 640 GB hard drive.
BUT, i took it to the apple store and they said I should return it because...
1) the screws on the bottom meant the seller refurbished it because they arent apple screws
2) the hard drive failed their test which was sad for me to see
3) the RAM sticks are two different sticks, one apple stick and one something else
4) the keyboard only lights up in the middle which the apple people think is water damage but they cant really tell without opening it. they wont open it because of the screws.
The reasons I dont think I should return it are....
1) I can get a squaretrade warranty so if it does break I can return it
2) $525 for a 2011 mac laptop is sooo good and unheard of, but I may be able to find another similar deal on craigslist so this might not be a valid reason
3) i've been heavily using it for a week without any issues
4) i dont want to spend more new hours searching for a laptop
5) i might not be able to find one on time for when school starts
BACKROUND INFO #1: it has ZERO dents, scratches, or dings - nothing else except whats listed above is wrong with it
BACKGROUND INFO #2: I am a college student who has had 7 PC's crash in the past 5 years. I gave up on PC and invested in this mac. I'm tired of losing my files and forgetting to back it up into my emails every week.
so looking at all that, what do you think I should do? AKA if you were in my shoes you would do what?

Answer 1

Now you know why it was $525.  Also realize you are getting a computer that isn't a warranty computer.  How much did you save?
Read the fine print on the Squaretrade warranty.  Make sure they won't turn it away for the same reason Apple does.
Can you live without the light?  Even if it got wet in the past it boots now.  If I buy a used car and the radio doesn't work but I get it for a really good price then I figure that's part of it if I can live with it and it doesn't interfer with day to day use.
It would be nice to know why the hard drive failed their test. Obviously if the computer boots it isn't total toast.  Clearly somebody has been inside the computer to add RAM and maybe change the drive?  That doesn't freak me in a used computer.
Maybe somebody can comment on non idential RAM but with some computers with RAM from a reputable upgrade source it doesn't matter.  Post the exact specs of the second chip.
My only question is, how up-front was the person from whom you bought the computer?  Did they tell you about the light?  It isn't a critical part but it is something you can assume to be working unless they tell you it isn't.  If they didn't, what else didn't they tell you?
Screws will freak Apple Service because they only look at stuff where they know 100% what's been done to it and nobody not-certified has messed with it.  I have done all kinds of things to my computer that would have voided the original warranty 20x over but it long ago went out of warranty.  It purrs.