Just act in good faith and GDPR will not bite.
Do you have $20million to make that gamble?This is a european thing, if any law says $x is the max fine or alike, then for a first time offense you usually get much less.
now understand that fines are proportionate to the offense. Are you engaging in doing very bad thing to personal data on a very large scale and having a business based on this ?
no ? then what are you afraid of ? that failing to answert to one guy asking for what data you have on him will cause you to be fined to bankruptcy level ? I pity the fool as said that one guy.
https://government.diginomica.com/2017/08/10/ico-maximum-fin...
Then again you can stop brandishing this FUD as this kind of fine is not gonna happen to small actors. If you act in good faith and are found doing something wrong you'll receive a notification asking you to fix the issue.
Why do people think EU is dumb and will start distributing 20M fines right and left at the first offense ? Just look at how it's done up until now and what CNIL said about how GDPR will be applied.