HN user
How Professionals do it: Bloomberg subscription ($1500/month) + CapIQ ($1000/month) + sell-side equity research reports + industry-specific research reports + excel add-ins + network of management, friends. They know exactly how their valuations differentiate from other professionals'.
How we do it: Talk about ratios, try and read articles, etc.
The short interest is only indicative of how many investors think that there is a greater chance TSLA is overpriced vs. underpriced. The short sellers may very well believe in Elon but they may also think that they have a superior risk-reward by shorting the stock right now. The high short interest is also indicative of investors having access to more ambiguous data, which is the case for a unique company with negative cash-flow and large market potential.