It's also possible that "downtime" has different meanings to different people. The client may be seeing "downtime" as the net result of what happened the last few times the server was "down," which could have been for any number of reasons (potentially even unrelated to the server itself).

When you get clients describing things like this, it's possible they've been promised things about this server before by other consultants that didn't pan out. They don't want to give you the full details because then you'll recommend a different route that they don't want to take (justifiably or not).

It's easier for them to frame the problem to a consultant in a way that allows for only one potential solution, even if perhaps better ones exist, because the guy in charge of making the decision isn't technically skilled enough to assess whether others proposed by consultants are as viable.

And, of course, one might read a little into why there exists a "boss" with such a highly-critical IT need that is hiring a consultant to do work like this, and thinks that threatening to not pay at all if there is any downtime is the best way to do it.

I mean, what if they opened the door to this closet and it grazed a power cable on the floor and the machine just shut off? Why even bother staying around to bring things back up? It wasn't your fault and there's already downtime: you're not getting paid.

Someone upthread was talking about how, as a Salesman, you have to read the room and know how to talk to clients. I did that for awhile, and always got a lot of mileage out of asking the customer what they ultimately wanted to accomplish, which usually revealed that what they were asking for was a solution to a self-made problem, and there was a better alternative altogether.

You cannot compare it to zero. You have to compare it to the cost of doing it with the downtime. There would be cost to that as well. It will not be free.