Fourth, the subjective theory of value is wrong. People can be defrauded. Theranos is a recent example of this. People can also be mistaken about value. The housing crash or the numerous failed investments in start-ups are clear examples of this. When people are defrauded or are mistaken, this means their belief in something being a value is wrong. Just because a lot of people believe that something is a value doesn’t make it so.
I don't think that existence of fraud disproves subjective theory of value. From the point of view of defrauded people, they are having a good deal, and if they knew the truth, they would change their evaluation.
Stocks can be analyzed by looking at performance of the company, state of the market and so on, and then calculating how much should they be worth, based on expected profit, but if a company lies about the state of its operations, you will get defrauded, even though you used math to calculate "objective" value.