50 years ago my grandfather bought 200 shares in a company that was starting. I currently have the certificate for those shares, still in his name. The company is still working and boast a multi-million dollar inventory. This is a private company, but it looks like they are selling internationally and doing well. What could be the potential of these shares and would it be in the companies best interest to buy them from me?

There are unknowns in this problem. Unless you know for sure you have just 200 shares then you don't know where you stand with it or the value of it. The reason Im saying this is because many times to get cash a company will split stock. You can either do a history research on it yourself or go through a broker to find out. You could be holding onto 2000 shares at this point and not know it.

Alternatively, it's also possible that the shares you have are worthless or highly devalued or maybe even worthless (if for example the company had a bankruptcy along the way, or if they issued additional shares to raise cash, which would dilute the value of the original shares). Like Califdadof3 says, you will have to do some research to find out.