How do I know which federations I can trust?

You should always use federation wallets in proportion to your level of trust in the federation and, by extension, their guardians. There are many ways to establish trust, some of which are covered below:

• You can run your own federation or know the guardians of a federation personally.
• You can lean on the social proof of public federation ratings shown on Bitcoin Mints and Fedimint Observer.
• You can rely on more indirect data points also shown in Fedimint Observer, such as the length of time a federation has been running, the number of guardians running it (and their server statuses), average transaction activity, or assets under management.