insusceptible
unsusceptible
blind
cautious
closed to
deaf
disinclined to believe
disposed to doubt
dogmatic
guarded
hard of belief
impersuadable
impersuasible
impervious
impervious to persuasion
inconvincible
incredulous
inflexible
leery
obstinate
positive
shy of belief
skeptical
suspecting
suspicious
unamenable
unconvincible
uncredulous
unimpressionable
uninfluenceable
unmovable
unpersuasible
unpliable
unreceptive
unresponsive
unsuggestible
unswayable
unwilling to accept
unyielding
wary