Most selection processes involve some kind of contact with other institutions who can provide a reference for their supplier. This might take the form of a questionnaire, a telephone call or a site visit.
A reputable supplier will have a good relationship with their reference sites and never use them without prior permission. The institution requesting the reference also needs to be conscious of how much time this takes particularly if requesting a written response as part of an ITT or requesting a site visit.
You can also draw on the collective knowledge of professional networks such as those that exist within ucisa and the Heads of e-Learning Forum (HeLF) and gain informal information from users who have not been specifically referenced by the suppliers.
Have you thought about international comparators as well as other UK institutions? London Business School looked at market trends globally as part of their research and had a particular eye on what similar institutions in the US were doing.