Denting or buckling; an onomatopoeic word expressing something giving in or collapsing under pressure.
車のボンネットがぶつかってベコベコになった。
The car's hood was dented after the collision.
古い缶が踏まれてベコベコ音を立てた。
The old can made a buckling sound when stepped on.
床が古くて歩くとベコベコする場所がある。
There are spots on the old floor that give underfoot and creak/buckle.
Bowing repeatedly; kowtowing or being excessively servile (archaic usage).
家臣たちは主の前でべこべこと頭を下げた（古い記述）。
Vassals bowed repeatedly before their lord (an old account).
彼は恩を売るために客の前でべこべこしていた。
He was fawning and bowing repeatedly in front of the customer to gain favor.