Proof of Concepts (POC) have a reputation of being long drawn out processes, therefore many vendors discourage going down this path. This however  does not have to be the case and is an essential step in confirming the correct and most cost efficient solution for your organisation.  Unless your organisation has processes that are very complicated and a long way off what is standard, then there is no need to test functionality at this stage.  The majority of Service Management solutions work very well and rarely encounter issues where what is sold from a functionality perspective cannot be delivered; instead the support model and pricing model is what requires testing to gain a full understanding of true costs.