Yah, it was one of the reasons I negotiated and priced around a CPO vs 3rd party Warranty in advance. I had the suspicion they were trying to coerce me into the maintenance as a way to make back their profit on the CPO price I negotiated. I told them no, but figured I'd research it to make sure.

No place in any of the paperwork I signed or on bmwusa.com can I find any reference that maintenance has to be performed by a certified mechanic.