CMS packages are complicated. It's difficult to select the right one through proposals and demos alone. Given the choice, most buyers would like to try out a commercial package before buying. RedDot-UK comes close with a 2-day gig where a consultant comes to your firm and converts part of your site to their system. They don't seem to actually install the product, but the try-out could still be useful. We imagine Microsoft CMS integrators would gladly reciprocate. At a higher, enterprise level, you might want to see how the packages actually work on your gear and network over a multi-week competitive "bake-off" between your two finalists, as Andy van Etten recommended earlier on this site. It's a bigger commitment for all parties (and might cost you money too), but it depends on how much it's worth to you to know you made the right choice....
Check out the "RedDot Challenge"          Read van Etten's Article