honoring AS-path prepend from a peer or customer?

Sanjay Dani wrote:

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?

I don't see why any sane provider wouldn't honor AS prepends,
although I'm not sure how one could actually manipulate AS_PATH
without proxy-aggregation, "private AS" or the like .. or some
hack to BGP source code, although it'd be unlikely to run in
any production code... Don't believe anyone would do exactly
what you suggest here though..

Of interesting things you should ask your provider to to support
when considering your ability downstream to influence "upstream"
path slection, the RFC1998 stuff is really nice..