I am considering buying a used Motorcycle Ninja Kawasaki....?
 

It has been sitting in the garage for about 3 years without being turned on at all. It is my girlfriend's sister's bike but soon after she bought it her father pulled the ground cable out and has not been moved since. what are the probable engine issues with a motorcyle like this and is it worth buying it and getting it repaired? Selling for 1000. Not sure of engine size.

Depending if they stored it properly for long term, definitely do not just try to add gas and start it! You could cause cylinder damage. I would talk to a local motorcycle mechanic and explain to him what you have. Most like he would recommend you taking it to him on a trailer so he could properly get it ready to start and run. You will most likely have to rebuild the carbs, which can be costly, a new battery, maybe tires (depending on the dryrot). But the biggest thing about starting a bike that has been stored is lubricating the upper motor so you don't start it dry. But doing all of that may cost more than just buying a running bike for a little more. But good luck!

even if you junked it and sold it on ebay you could get more than that out of it, i junked a non running Honda shadow and made $1700.00 of ebay for this thing.You to try to fix it or have someone look at it but i think it's worth the money unless it's ragged out

don't by it you will have to many problems with it and the relation ship with the family will destroy