Sure, a heads-up is certainly nice, but I don't think that running a (reasonable) set of benchmarks is all that out of the ordinary, or any different from just taxing the service at 100% with some periodic batch job or the like.
Paying for it is even stranger IMO.
And for what it's worth, I did actually work for a few small SaaS businesses, but a few reasonable benchmarks wouldn't have been a problem.
Of course, if your benchmarks are going to take 50 hours it's a different story.
Also: I suspect a lot of these database SaaS services are a lot smaller than you'd might think. I know at least one of them is anyway because I worked there (and there's no DeWitt Clause).
