Is an custom field accesible via URL/Search query etc.?
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I'm going to set up a webshop, that sells domain names.
Every domain is a single post, and every post contains about 10 custom fields.
My question is, are these custom fields accesible if I don't query them?

For example, you go to a single post (a domain overview in my case) and can you retrieve the values of my custom fields? Otherwise people can retrieve the code, without paying for it. Are those custom fields accesible if I don't query them, or not all of them? 

Is it safe to keep the code's where you pay for in a custom field?

Thnx in advance!

Thomas