You do not require "direct" evidence to prove a crime. A conviction resting solely on circumstantial evidence is sufficient. Classic example: Baby is heard crying. Man walks into the room, kills baby. Baby is no longer crying. Witnesses see man walk out with bloody hands. No direct evidence is necessary. A second example is if there's text messages from you saying "Come over, I've got 5 grams of Cocaine", and people see your client come over. Immediately after leaving, they find 5 grams of cocaine on him. Its reasonable to say that you are the dealer.
DISCLAIMER: This is for INFORMATIONAL PURPOSES ONLY and should not be relied upon as legal advice. Please contact a local attorney for legal advice.