I tell customers that technically, it is THEIR lease and they are responsible for the return. However, that the unwritten rule is the person who secures the business should return it for the customer. If you know a machine like that exists, add the cost to your quote and make sure that it is known that you will return the machine for them. If the other guy hasn't figured that in and gets asked, they either have to:
1. Look like bad guy to charge an extra fee
2. Tell them it's their responsiblity (makes it look like they aren't doing everything to take care of the customer)
3. Or say they will do it, eat the costs and have me mentioning that they didn't do this upfront (what other costs are they NOT going to mention).
And some customers say they will return it on their own and it's done. The key is to pull this issue out in the light and deal with it FIRST.