Their are an awful lot of NES systems that are broken. The connector pins get bent and you have to replace them takes about $15 and 20-30 mins worth of simple work.
Also it is perfectly safe to blow into a cartrige, clean it with rubbing alcohol or air duster. I do it all the time when I buy carts from yard sales.
One time I was cleaning the carpet and moved all my stuff onto the back porch. Low and behold my copy of Metal Gear didn't make it back in the house. About three months later I found it underneath the porch in two inches of mud after it had rained, snowed, and sustained sub 0 C temperatures for a couple weeks. To my amazement I cleaned it up (I took the cart apart with my game tool) with air duster and alcohol tested it in my top-loader and by god it started right up. No joke. The Cartriages themselves are practically indestructible.
