Whereas state cases may include one or two controlled sales to a confidential informant, federal cases tend to be very detailed and involved. Often, they will involve extensive wiretapping, where federal agents listen in on conversations and try to record the setting up of a drug sale or transaction.
Because the federal government also has extensive resources, these investigations can involve locating the source of the drugs, including their country of origin, how they were trafficked to the country, and then how they were transported once inside.
Finally, federal law enforcement may utilize individuals who are part of a trafficking scheme and use them as informants. They may provide valuable information about who is involved, what drugs are being sold, how much, and in what ways. Often this is in exchange for leniency against them.