If you make it available to someone, they can copy it.
You could make it harder for someone by only allowing specific data to be viewed. Example:
If you had a part number/price list with a million lines in it, don't display it all like this:
Part Number 0001 - $5
Part Number 0002 - $9
Instead, return a single price for a specific part number that's requested.
In the end though, people will get what they want, so don't inconvenience 100 good users/customers just to annoy 2 or 3 idiots.
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