You can not trust anyone except yourself, but you don't have to. According to the man page, you can even run your own private tor network! Obviously you have to edit your torrc file.
From the man page:
FallbackDir ipv4address:port orport=port id=fingerprint [weight=num] [ipv6=[ipv6address]:orport]
When we’re unable to connect to any directory cache for directory info (usually because we don’t know about any yet) we try a directory authority. Clients also simultaneously try a FallbackDir, to avoid hangs on client startup if a directory authority is down. Clients retry FallbackDirs more often than directory authorities, to reduce the load on the directory authorities. By default, the directory authorities are also FallbackDirs. Specifying a FallbackDir replaces Tor’s default hard-coded FallbackDirs (if any). (See the DirAuthority entry for an explanation of each flag.)
Use Tor’s default hard-coded FallbackDirs (if any). (When a FallbackDir line is present, it replaces the hard-coded FallbackDirs, regardless of the value of UseDefaultFallbackDirs.) (Default: 1)
DirAuthority [nickname] [flags] ipv4address:port fingerprint
Use a nonstandard authoritative directory server at the provided address and port, with the specified key fingerprint. This option can be repeated many times, for multiple authoritative directory servers. Flags are separated by spaces, and determine what kind of an authority this directory is. By default, an authority is not authoritative for any directory style or version unless an appropriate flag is given. Tor will use this authority as a bridge authoritative directory if the "bridge" flag is set. If a flag "orport=port" is given, Tor will use the given port when opening encrypted tunnels to the dirserver. If a flag "weight=num" is given, then the directory server is chosen randomly with probability proportional to that weight (default 1.0). If a flag "v3ident=fp" is given, the dirserver is a v3 directory authority whose v3 long-term signing key has the fingerprint fp. Lastly, if an "ipv6=[ipv6address]:orport" flag is present, then the directory authority is listening for IPv6 connections on the indicated IPv6 address and OR Port. Tor will contact the authority at ipv4address to download directory documents. The provided port value is a dirport; clients ignore this in favor of the specified "orport=" value. If an IPv6 ORPort is supplied, Tor will also download directory documents at the IPv6 ORPort.
If no DirAuthority line is given, Tor will use the default directory authorities. NOTE: this option is intended for setting up a private Tor network with its own directory authorities. If you use it, you will be distinguishable from other users, because you won’t believe the same authorities they do.
When configured to use both directory authorities and fallback directories, the directory authorities also work as fallbacks. They are chosen with their regular weights, multiplied by this number, which should be 1.0 or less. The default is less than 1, to reduce load on authorities. (Default: 0.1)
AlternateDirAuthority [nickname] [flags] ipv4address:port fingerprint
AlternateBridgeAuthority [nickname] [flags] ipv4address:port fingerprint
These options behave as DirAuthority, but they replace fewer of the default directory authorities. Using AlternateDirAuthority replaces the default Tor directory authorities, but leaves the default bridge authorities in place. Similarly, AlternateBridgeAuthority replaces the default bridge authority, but leaves the directory authorities alone.