I'm rereading Liberation in Palm of Your Hand and found this helpful instruction on pages 278 and 279. I've summarized it into bullet points:
1. Buddhas manifest themselves to benefit all beings
2. We cannot perceive Sambhogakaya forms and would not listen to the instructions of a manifested Buddha in the form of a ditch digger. The best form to benefit beings is that of a Guru
3. Therefore, our Guru is a Buddha
5.If we have several Gurus, at least one is a Buddha
6. If we try to find the Buddha by examining our Gurus' faults we will find reason to disqualify them all
7. Therefore, we should consider all our Gurus as the Buddha. Which they probably are.