honoring AS-path prepend from a peer or customer?

If a peer (or transit customer) prepends their own AS to
their route announcements to you, do you ever strip off
the excessive As'es? That is, do you always honor them
in your announcements to your other customers (or peers)?

I do understand that any operator has full control over
deciding his own outbound policy, regardless of the
AS path.

I want to know what the industry practice is and whether
I should stipulate in my next upstream agreement that
they honor my prepends?