Explain that the miraculous signs mentioned in Mark 16 (driving out demons, drinking poison) were not performed to prove a believer’s faith or that one has a "special anointing," as taught by the Church of God with Signs Following sect, but instead they were meant to confirm the truth of Christ’s message.
Bernard Orchard’s A Catholic Commentary on Sacred Scripture explains the miracles of Mark 16:17-18 in this way:
When sending the Apostles on a temporary mission in Palestine, Christ gave them power to cast out demons in order to strengthen the appeal of their preaching. Now he promises to believers miraculous signs to guarantee the truth and divine origin of the doctrine which they had accepted (Heb. 2:4). The promise is made to the community of the faithful rather than to each individual believer. In the early days of the Church, possibly because of a skeptical and hostile world to which the Gospel and Church were still new, some of these manifestations more frequent than in later times. But Christ’s promise is not limited to a particular period. In every age miracles have given proof that Christ abides with the Church.