I can see that there are many different opinions about this, but I think this raises an important question to startups that start free and plan to convert into a paid service on how it should be done the right way, without upsetting customers.<p>IMO, I think it depends on when they made these plans. If this was their path from the beginning and the service was free for a specific reason, I think it should be clearly pointed out on the website that the service is free for only a specific period of time.<p>If the plan of charging customers was added later on (after customers stared using the service), the solution would be to: definitely don't charge customers without them opting in, even if you send them an email, even if you wait for some days after to start charging. Changing customers to a temporary "trial" phase would be a good idea I think. This way, customers will know that they need to pay when they use the service the next time.