at the mercy of
• completely in the power of.
• "consumers were at the mercy of every rogue in the marketplace"
Similar:
in the power of,
under/in the control of,
in the clutches of,
in the palm of someone's hand,
under the heel of,
subject to,
defenceless against,
unprotected against,
vulnerable to,
threatened by,
exposed to,
susceptible to,
prey to,
(wide) open to,
an easy target for,
