Did you read page 8 of the consultants guide? There is a section "Customer Preparation" with many details. Remember you are not just after technical information, you need to ensure there is space and facilities for you to run the onsite work (room, projector, access to systems) and who is going to be participating from the client.

There are some good things to go through in the guide. In addition I also like to get an understanding of why they are having the Healthcheck done? Do they have large problems or issues currently? Are they wanting to validate an install performed by a 3rd party? Are they trying to fire their VMware Admin and they after a report to prove they have been doing a poor job. Its always good to know if you are walking into an "agenda".

Hope it goes well for you.

Considering awarding points if this is of use