Ask HN: Is Mockup Data a thing you can ask from SaaS Salesperson?

My accounting client is asking me to help evaluate a third Point of Sale (POS) in seven months. They actually signed on to the first one, and are desperately unhappy with the results. The promised solutions are ineffective and the API integration to the ERP insufficient.

Which raises the question in my mind, do any SaaS providers offer to "mock up" the solution with some examples of difficult to structure sales items (not the full product list)? Produce example reporting for evaluation? Common sense would say there is no division in any high-flying POS company which does this sort of work. The company's organization drives customers into contract quickly, run it through provisioning, and then deal with contract if the result is no joy.