Will your service save your target customers time and make their lives easier or make their work more effective? If so, charge for it! Even if only a small amount, don't undersell yourself. If its not worth paying for, they probably won't use it for free either. You should definitely consider a free trial if nothing else but keep it in their minds that your service offers value. If you have paying customers you will also be much more likely to devote yourself to improving the service and seeing it through to full fruition. If a prospect converts to being a paid customer, they will be invested in using the platform and continuing to validate what you are doing.