Why is it bad DSLR Nikon D60 buying it used?

My teacher knows a lady who's daughter is selling a nikon D60 slr camera for $350 with original receipt included, all the package with straps, Nikon AF-S 18-55mm f/3.5-5.6G DX VR lens included, plus two year warranty and one year of using camera. I was wondering is it good idea doing so? I know that my teacher knows that lady who's selling the item, plus I talked to lady only on the phone, and I think next week I will be purchasing the camera. I'm not good at cameras at all, plus it would be my first slr camera. Although I have money to buy something new like Nikon D90 or Canon T1i, which those both can shoot video and have other great features. The camera originally cost $750 with three year warranty. What should I look in buying an used camera nikon d60?

I'm wondering the possibilities that the camera won't work well, but if it does can I with two year warranty have actially replaced by manufacturer because it still have like two years of warranty on it.
I'm needing the camera only for the class and not for my own personal use.

Posting a question once is enough.

Cameras that are refurbished by the OEM are going to last a long, long time.

On of the best sources for refurbished Nikon dSLR's is Adorama

Manufacturers usually provide a 90 day warranty. Any longer warranty is provided by the seller

Read the fine print and determine if the camera was actually refurbished by the camera maker or someone else

If you don't know anything about cameras and you're buying used you are taking a slight risk.

PErsonally I fail to see why you would buy a D60 if you can afford the much better D90.