Jim Cramer interviewed Alibaba CEO, Jack Ma, Friday morning on CNBC as the company made its debut on the New York Stock Exchange. Cramer gives his impressions of China's richest man saying he found him to be humble and without a lot of flash. As for investors who want a piece of Alibaba, Cramer says they first have to understand the process. Investors coming in now at the opening are not going to get as good an average as a big institution in terms of pricing. Cramer says $90 is where he begins to think the e-commerce company is overvalued; at $100 it becomes Twitter-like where it should be valued as a Facebook instead. He says Alibaba stock is not a bargain between $90 to $100 and people who care about valuation will sell it there.