Finding asymmetric path

[ml at kenweb.org (ML)]

Randy Bush wrote:
>> I'm reasonable certain a customer of ours who is using one of our 
>> netblocks is using a different reverse path to reach us.  How might I 
>> figure out who is allowing them to source traffic from IPs that belong 
>> to us?
> 
> you are implying that they are not allowed to multi-home using the ip
> space you have assigned to them.  good way to lose a customer.
> 
> randy

Does it count as multihoming when we are the only ones announcing the space?