AMT you HAVE to give a customer a refund if they ask on the preorder. Don't worry about what other companies do, most of them are shit. If you don't have the money to refund a few customers who aren't patient, you shouldn't be running this business. There are laws about this, call the FTC and ask them if you can indefinitely keep customer funds for preordered product that you are using to finance your startup business when they ask for refunds... Don't be another scammer, when a customer wants a refund you give it to them and sell their "spot" to someone else. Anything less makes you suspect. You should not have entered this business without enough financing to secure the product before sales.
Also, people. If you don't get a refund on a product like this, initiate chargeback proceedings with your credit card immediately. If you paid in bitcoin, go to your local courthouse and file a lawsuit in small claims court for the amount you paid. Don't be stupid and wait for someone else to do it for you. Make noise, get noticed, and watch how quickly the company sends you that refund.