Buying it is probably the worse decision you can make. Search this section with keywords "RROD" and go through them and you'll realize there is no proper fix.
I am telling you because a friend got screwed and here is the link to it:
http://www.techenclave.com/consoles/xbox-360-rrod-problem-106459.html
He tried the Xclamp trick and ended with a mess. Result sold it to raddiwala. The funniest thing is he had bought it on installment basis and was paying for the next few months.
Bottomline: RROD cannot (hardly ever) be fixed. If you want to try your luck go ahead but if I was you I would stay away from it.