Possible Clues:

• He doesn't believe in aimless coasting
• Not knowing cost, gain on exchange
• Lacking faith in God
• One doubts a rough costing
• Not knowing what to believe and acting so strangely
• A sceptic acting so oddly
• One doubts coasting is all at sea
• Incredulous person confusing gain with cost
• Carol's up in a short moment? One doubts
• Person of uncertain faith makes saint go mad, more or less (8)