Often you get a prospect who is eager to get the product, test it, and evaluate it, but they don't seem to get their act together. It might be that they can't get the right kind of hardware, test environment or meeting rooms, for you to come on site and show how great your product really is.
This rings alarm bells for me.
If they can't manage the infrastructure for a test or evaluation, does the prospect have the right executive buy-in to actually purchase and use your product?
Going in too early to prove that your product works in the customer's environment (also known as Proof of Concept or PoC) sometimes takes you further away from winning the deal. The problem is, you are probably appeasing the wrong audience by running an early PoC. The correct audience is the buyer or final decision maker. Unless they are sponsoring the final evaluation, you set yourself up for a later, more comprehensive exercise, potentially with very different success criteria from the first one.
Use the Proof of Concept as bait to find the right people in the organisation, and don't let them have the proof until you know the buying process from there on. If there is a higher authority, see if you can get them involved in the PoC process or at least let them know that this is going on. If they want something to do with the purchase of the product, then you will want to know what they need to see to become a buyer.
Have a checklist or PoC Sign-Off document ready for your customer showing ideally how they would prepare for a proof of concept, the kind of success criteria you expect to fulfill (and use their requirements as you are aware of them - in their own terminology). Get the buyer to sign the document to get the understanding on both sides that if the product does what they want, then they will buy it. If they are unwilling to sign this, chances are that you haven't found the actual buyer yet!!!
If the customer wants to Pilot or do some further Evaluation with less of your help, ensure that you set some kind of boundaries on the use, and measurable success criteria that you can help the customer evaluate. Remember the product is yours. Until they buy it, they don't actually get any rights to use it. Imagine that you are handing over the keys to that Bentley (like the one you hope to buy with the commission) for them to take it for a spin. Don't you want any assurances that it won't be mis-used.
Even though PoCs are normally free of charge, don't undervalue their use - they can be a powerful part of your toolset - but question if it is the right time to do one. Usually you only get one crack at it - so make sure it is your best shot and at the right time.