It's been a week since smiling Uber executives rang the opening bell at the New York Stock Exchange. But out on the trading floor, there were whispers about the company's finances and business model. 

Uber shares have had a rough first week of trading, dipping as low as 36 U.S. dollars from their listing price of 45 U.S. dollars. Some analysts say Uber's initial public offering was set up for disappointment after being hyped-up.

"The fact that Uber's IPO was not the success story that it should have been isn't really about the fundamentals of the company today. It's more about the fact that their valuation got too high too fast in the past and that severely constrained their ability to set a fair price for their IPO when they went public," said Arun Sundararajan, professor of business at NYU.

Uber's CEO Dara Khosrowshahi put the disappointing IPO down to the U.S.-China trade talks, which hit an impasse the very same day Uber went public. But he insisted the company is measuring success in "five to ten years, not in one day."

Other Wall Street insiders, though, see some weaknesses in Uber's fundamentals right now. In 2018, the company's revenue was up by 43 percent from the year before, but that growth in revenue is slowing down.

"That's a huge problem for a company valued at 80 billion U.S. dollars, which is what they wanted to do at the time. With profits, we can wait. We'll believe you, we'll give you the benefit of the doubt about profits. But, revenue? That's your thing, you've got to grow that," said Santosh Rao, head of research at Manhattan Venture Partners in New York.

This year, Uber has been paying out around 100 million U.S. dollars per month in driver incentives. They encourage drivers to stick with Uber, instead of switching to Lyft or another competitor. The more drivers there are, the fewer time customers spend waiting for a ride.

However, analysts say Uber can't keep pumping that amount of cash into driver incentives forever.

"Ten years from now, if Uber is still spending the same amount of money on driver incentives, then they probably won't be in business. They have to build both passenger and driver loyalty, in ways other than paying them more to drive on our platform or charging below cost to use our platform," said Arun Sundararajan from NYU.

Just before Uber's IPO debut, drivers around the world went on strike for better wages and working conditions. Uber has already tested its vision of self-driving cars replacing those protesting drivers, but like profitability, that could still be several years down the road.