I've done jobs like this and been just fine. Establish t&m, establish that you are a consultant, establish that there is no nstallation warranty.

Sit down with them, decide on a game plan, decide what equipment they insist on sourcing themselves, what you will provide. Let them know you dont know the ins and outs of every product in the world, and that the project will go easier if they work with you to use the products that you recomend.

If they insist on doing their own control, let them do it.