[webstartupper]

If you are offering a trial, let it be the best experience for your potential customers. A simple way of ensuring they do not abuse the free trial is to take credit card upfront (or setup a paypal subscription to start charging them 14 days later)

You could also have the trial based on how many files they can process instead of how long they have access. If it takes only one file for a potential customer to have the aha moment, enforce a "one file" trial. If it takes three, let it be three.

From what you've said, your service lets people extract data from files. Unless your customers have an ongoing need to process files, it might make sense to test a different pricing strategy instead of a SaaS one. This may also help you differentiate from your competitors who I presume have SaaS plans as well.

Also, if you can post a link to your service, maybe HN can give you better advice.