You can operate from the standpoint that most people will be honest (which is the correct assumption). Grant them a given set of corrections before they can con

You can operate from the standpoint that most people will be honest (which is the correct assumption). Grant them a given set of corrections before they can contact you. For example, charge them $99 per label with up to 5 corrections. If they need a correction afterwards then have them email you. Which at that point they will be looking at a new label anyways (charge them again). Anyone can modify the PDF file and change the settings. What they need is access to the nutrients calculation logic (which is the actual product you sell). Or you could do like it is done with barcodes, and charge a low fee per label generated. Say $20 for every label with no corrections. Just state it very clearly in there. Twenty dollars is low enough that they won't try and scam you out of things. Plus you can also sell them a package deal where for $99 they can get 6 labels (5+1 free). It will make sense in their heads because the $99 deal seems to be the better value. So: $20 per label or $99 for 5 labels plus get one FREE.