There are many karmis in the dress of devotees, but the Supreme Personality of Godhead can detect their purpose. The karmis want to use the property of the Lord for their selfish sense gratification, but a devotee endeavors to use the Lord's property for God's service. Therefore a devotee is always distinct from the karmis, although the karmis may dress like devotees.
Ref. VedaBase => SB 8.9.28