The sign of perfect surrender is a state of inner Peace in all circumstances. There is also freedom from desire and the egoism of Nature. This brings inner felicity which is another sign of surrender.
Doubt of course act as a bar to spiritual progress. However we can replace them with a genuine seeking, an effort to understand the Divine Ways and the Divine Wisdom behind the luminous words. Doubt closes the doors whereas seeking opens it.
Affectionately,
Alok Da