system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: how are Forbes able to estimate/calculate the wealth of the people on their billionaires list and how accurate is it?
gpt
>This is our 29th year publishing the Forbes Billionaires list. Though we’ve been at it a long time, it is never an easy task. Our reporters dig deep and travel far. To compile net worths, we value individuals’ assets–including stakes in public and private companies, real estate, yachts, art and cash–and take into account estimates of debt. We attempt to vet these numbers with all billionaires. Some cooperate; others don’t. We also consult an array of outside experts in various fields. The Forbes Billionaires ranks individuals rather than multi-generational families who share large fortunes. So Maja Oeri, who has a disclosed stake in pharmaceutical firm Roche, makes the list, but her eight relatives who, with a nonprofit foundation, share a multi-billion fortune do not. In some cases we list siblings together if the ownership breakdown among them isn’t clear, but here, too, they must be worth a minimum of $2 billion together to make the cut. We split up these fortunes when we get better information, as we did with the heirs of Colombia’s Julio Mario Santo Domingo this year. Children are listed with their parents when one person is the founder and in control. Those fortunes are identified as “& family.”

>We do not include royal family members or dictators who derive their fortunes entirely as a result of their position of power, nor do we include royalty who, often with large families, control the riches in trust for their nation. Over the years Forbes has valued the fortunes of these wealthy despots, dictators and royals but we have listed them separately as they do not truly reflect individual, entrepreneurial wealth that could be passed down to a younger generation or truly given away.

TL;DR: Using dozens of sources they value everything the billionaires possess, including debts, and compile the values. They attempt to vet the values with the individuals and some agree while others don't. They have a team of financial analysts listed on their website and other consulted experts in various fields.