AI files from client have multiple copies on top of each other.

I receive files from clients, sometimes AI, sometimes PDF. When I open them there are frequently multiple copies of the work ontop of each other. As in, if I select a line and delete it, there is a duplicate still there, like they hit copy then pasted 2-3  times on top. it is super frustrating when trying to manipulatre artwork for production.

Is there a way to stop this, or quickly delete all but one copy?